Perhaps you are thinking of Vintage plates in Washington state.
I believe the details are that you pay a one time fee to register it as an antique or vinatage car ( 25 years old sounds low, but it could be ) and then there are no yearly fees after that.
However, I don't think that's for regular use.  I think that's intended for club use, and limited to so many miles a year , like 2,500 a year.
what's the Wa dmv site ?........
wadmv.gov  something like that.
you could read it about it there.   
yeah, this is the offical govnmint site :
http://www.dol.wa.gov/

and I just  stumbled on this one .........first time I've ever seen this ........
it's an unoffical guide to the Wa DMV.
might be some gems in there.
http://www.dmv.org/wa-washington/department-motor-vehicles.php

scott
formerly of western washington- Port Townsed -  served 4 years there and then escaped. 
scott
www.turbovans.com 
  ----- Original Message ----- 
  From: Paul Connelly 
  To: Scott Daniel - Turbovans 
  Cc: vanagon@gerry.vanagon.com 
  Sent: Wednesday, July 16, 2008 3:34 PM
  Subject: Re: Annual Licence Plate Fee - 84 Westy

  That was an increase over last year too! - first time over $30 in the 4 years I've had her! I think on her 25th birthday we stop paying completely (don't quote me on that), then we are considered "Vintage".

  Paul.

  On Wed, Jul 16, 2008 at 4:22 PM, Scott Daniel - Turbovans <scottdaniel@turbovans.com> wrote:

    man...........that is what older cars should pay for a year's reg- some
    30-something kind of fee !
    right on.
    Hope they don't change that on ya !
    no complaints there.
    Conveniently, Oregon is two years at a time.  And just think of the office
    and admin time that saves, and the paper that saves !
    I do notice an extreme amount of redundant and unnessesary paper billing and
    invoicing going on - all of which likely will go straigt into landfill. (
    until they dig it up in a hundred years, if humans even exist then )

    scott

    ----- Original Message -----
    From: "Dave Creasy" <mkcdc@VERIZON.NET>
    To: <vanagon@GERRY.VANAGON.COM>

    Sent: Wednesday, July 16, 2008 2:04 PM
    Subject: Re: Annual Licence Plate Fee - 84 Westy

      In PA. our registration is $ 36.00.  I guess they think we need the rest
      for
      pot hole repairs....

      Dave C
      '78 Westy
      '85 Westy
      .93 EVMV
      ----- Original Message -----
      From: "Don Spence" <dkspence@TELUS.NET>
      To: <vanagon@GERRY.VANAGON.COM>
      Sent: Tuesday, July 15, 2008 5:13 PM
      Subject: Re: Annual Licence Plate Fee - 84 Westy

        $74.50 in Alberta.. But... if you want to register it as an Antique
        (25 years old) it's $32 for life. Some restrictions may apply..
        On 15-Jul-08, at 2:15 PM, Automatic digest processor wrote:

          Date:    Tue, 15 Jul 2008 14:06:19 -0600
          From:    Tom Buese <tombuese@COMCAST.NET>
          Subject: Re: Annual Licence Plate Fee - 84 Westy