21 or Older for Handguns

From Calguns Wiki

Both Federal law and California law restrict transfer of handguns to those 21 years old and older.

Federal Law restricts FFLs from delivery to under-21: US CODE 18 USC 922 (b)

(b) It shall be unlawful for any licensed importer, licensed
manufacturer, licensed dealer, or licensed collector to sell or
deliver—
(1) any firearm or ammunition to any individual who the
licensee knows or has reasonable cause to believe is less than
eighteen years of age, and, if the firearm, or ammunition is
other than a shotgun or rifle, or ammunition for a shotgun or
rifle, to any individual who the licensee knows or has
reasonable cause to believe is less than twenty-one years of
age; 

California Law restricts everyone: Penal Code 12072(a)(3)

(3)(A)No person, corporation, or firm shall sell, loan, or 
transfer a firearm to a minor, nor sell a handgun to an
individual under 21 years of age.

(B)Subparagraph (A) shall not apply to or affect those
circumstances set forth in subdivision (p) of Section 12078.

Penal Code 12078(p) exempts

• (p)(2): loans from a non-parent, with conditions
• (p)(3): loans from a parent, with fewer conditions
• (p)(6): purchases of antiques

In this context, 'antiques' are defined and Federal law and referred to by California law: 18 USC 921(a)(16)

The term “antique firearm” means—
(A) any firearm (including any firearm with a matchlock,
flintlock, percussion cap, or similar type of ignition system)
manufactured in or before 1898; or
(B) any replica of any firearm described in subparagraph (A) if
such replica—
(i) is not designed or redesigned for using rimfire or
conventional centerfire fixed ammunition, or
(ii) uses rimfire or conventional centerfire fixed ammunition
which is no longer manufactured in the United States and which
is not readily available in the ordinary channels of commercial
trade; or
(C) any muzzle loading rifle, muzzle loading shotgun, or muzzle
loading pistol, which is designed to use black powder, or a
black powder substitute, and which cannot use fixed ammunition.
For purposes of this subparagraph, the term “antique firearm”
shall not include any weapon which incorporates a firearm frame
or receiver, any firearm which is converted into a muzzle
loading weapon, or any muzzle loading weapon which can be
readily converted to fire fixed ammunition by replacing the
barrel, bolt, breechblock, or any combination thereof.

And, 12078(c)(2) allows Intra-Family transfer to 18,19 and 20 year olds.