Yes, it really is 30 years.  Once upon a time, it was only 25 years, but
the state legislature changed it to 30.  The following Q&A is from the
FAQ at <http://www.dmv.ca.gov/vr/smogfaq.htm#BM2536>

How old does a vehicle have to be to qualify for a smog exemption?

Vehicles with a year model 30 years old or older are exempt from the
smog certification requirements.

     Example: The calendar year is 2003- 29 = 1974 exempt year model

The current calendar year minus 29 equals the year model exempt from
smog certification.

Mike Snow

Jeffrey Schwaia wrote:
> FYI: Smog exemption in California is for '73 and older vehicles, NOT 30
> years and older.
>
> Last year, it was '73 and older, next year it will still be '73 and older.
>
> Cheers,
>
> Jeff