Here is the section with reference to age 16+, other sections of the vehicle code apply to children under the age of 16 all of whom must be ratrained, but not necessiarly with "seatbelts".
Vehicle Code section 27315.
(a) The Legislature finds that a mandatory seatbelt law will
contribute to reducing highway deaths and injuries by encouraging
greater usage of existing manual seatbelts, that automatic crash
protection systems which require no action by vehicle occupants offer
the best hope of reducing deaths and injuries, and that encouraging
the use of manual safety belts is only a partial remedy for
addressing this major cause of death and injury. The Legislature
declares that the enactment of this section is intended to be
compatible with support for federal safety standards requiring
automatic crash protection systems and should not be used in any
manner to rescind federal requirements for installation of automatic
restraints in new cars.
(b) This section shall be known and may be cited as the Motor
Vehicle Safety Act.
(c) (1) As used in this section, "motor vehicle" means any
passenger vehicle or any motortruck or truck tractor, but does not
include a motorcycle.
(2) Until May 1, 2000, for purposes of this section, a "motor
vehicle" also means any farm labor vehicle that was first issued an
inspection certificate under Section 31401 on or after October 1,
1999.
(3) On and after May 1, 2000, for purposes of this section, a
"motor vehicle" also means any farm labor vehicle, regardless of date
of certification under Section 31401.
(d) (1) A person may not operate a motor vehicle on a highway
unless that person and all passengers 16 years of age or over are
properly restrained by a safety belt. This paragraph does not apply
to the operator of a taxicab, as defined in Section 27908, when the
taxicab is driven on a city street and is engaged in the
transportation of a fare-paying passenger. The safety belt
requirement established by this paragraph is the minimum safety
standard applicable to employees being transported in a motor
vehicle. This paragraph does not preempt any more stringent or
restrictive standards imposed by the Labor Code or any other state or
federal regulation regarding the transportation of employees in a
motor vehicle.
(2) The operator of a limousine for hire or the operator of an
authorized emergency vehicle, as defined in subdivision (a) of
Section 165, may not operate the limousine for hire or authorized
emergency vehicle unless the operator and any passengers four years
of age or over and weighing 40 pounds or more, in the front seat are
properly restrained by a safety belt.
(3) The operator of a taxicab may not operate the taxicab unless
any passengers four years of age or over and weighing 40 pounds or
more, in the front seat are properly restrained by a safety belt.
(e) A person 16 years of age or over may not be a passenger in a
motor vehicle on a highway unless that person is properly restrained
by a safety belt. This subdivision does not apply to a passenger in
a sleeper berth, as defined in subdivision (v) of Section 1201 of
Title 13 of the California Code of Regulations.
(f) Every owner of a motor vehicle, including every owner or
operator of a taxicab, as defined in Section 27908, or a limousine
for hire, operated on a highway shall maintain safety belts in good
working order for the use of occupants of the vehicle. The safety
belts shall conform to motor vehicle safety standards established by
the United States Department of Transportation. This subdivision
does not, however, require installation or maintenance of safety
belts where not required by the laws of the United States applicable
to the vehicle at the time of its initial sale.
(g) This section does not apply to a passenger or operator with a
physically disabling condition or medical condition which would
prevent appropriate restraint in a safety belt, if the condition is
duly certified by a licensed physician and surgeon or by a licensed
chiropractor who shall state the nature of the condition, as well as
the reason the restraint is inappropriate. This section also does
not apply to a public employee, when in an authorized emergency
vehicle as defined in paragraph (1) of subdivision (b) of Section
165, or to any passenger in any seat behind the front seat of an
authorized emergency vehicle as defined in paragraph (1) of
subdivision (b) of Section 165 operated by the public employee,
unless required by the agency employing the public employee.
(h) Notwithstanding subdivision (a) of Section 42001, any
violation of subdivision (d), (e), or (f) is an infraction punishable
by a fine of not more than twenty dollars ($20) for a first offense,
and a fine of not more than fifty dollars ($50) for each subsequent
offense. In lieu of the fine and any penalty assessment or court
costs, the court, pursuant to Section 42005, may order that a person
convicted of a first offense attend a school for traffic violators or
a driving school in which the proper use of safety belts is
demonstrated.
(i) In a civil action, a violation of subdivision (d), (e), or (f)
or information of a violation of subdivision (h) does not establish
negligence as a matter of law or negligence per se for comparative
fault purposes, but negligence may be proven as a fact without regard
to the violation. (j) If the United States Secretary of Transportation fails to
adopt safety standards for manual safety belt systems by September 1,
1989, no motor vehicle manufactured after that date for sale or sold
in this state shall be registered unless it contains a manual safety
belt system which meets the performance standards applicable to
automatic crash protection devices adopted by the Secretary of
Transportation pursuant to Federal Motor Vehicle Safety Standard No.
208 (49 C.F.R. 571.208) as in effect on January 1, 1985.
(k) Each motor vehicle offered for original sale in this state
which has been manufactured on or after September 1, 1989, shall
comply with the automatic restraint requirements of Section S4.1.2.1
of Federal Motor Vehicle Safety Standard No. 208 (49 C.F.R. 571.208),
as published in Volume 49 of the Federal Register, No. 138, page
29009. Any automobile manufacturer who sells or delivers a motor
vehicle subject to the requirements of this subdivision, and fails to
comply with this subdivision, shall be punished by a fine of not
more than five hundred dollars ($500) for each sale or delivery of a
noncomplying motor vehicle.
(l) Compliance with subdivision (j) or (k) by a manufacturer shall
be made by self-certification in the same manner as
self-certification is accomplished under federal law.
(m) This section does not apply to a person actually engaged in
delivery of newspapers to customers along the person's route if the
person is properly restrained by a safety belt prior to commencing
and subsequent to completing delivery on the route.
This section does not apply to a person actually engaged in
collection and delivery activities as a rural delivery carrier for
the United States Postal Service if the person is properly restrained
by a safety belt prior to stopping at the first box and subsequent
to stopping at the last box on the route.
(o) This section does not apply to a driver actually engaged in
the collection of solid waste or recyclable materials along that
driver's collection route if the driver is properly restrained by a
safety belt prior to commencing and subsequent to completing the
collection route.
(p) Subdivisions (d), (e), (f), (g), and (h) shall become
inoperative immediately upon the date that the United States
Secretary of Transportation, or his or her delegate, determines to
rescind the portion of the Federal Motor Vehicle Safety Standard No.
208 (49 C.F.R. 571.208) which requires the installation of automatic
restraints in new motor vehicles, except that those subdivisions
shall not become inoperative if the secretary's decision to rescind
that Standard No. 208 is not based, in any respect, on the enactment
or continued operation of those subdivisions.
