Most of your 'old car' type magazines pretty much go with the 25 year rule for autos. Sure, there are some states who go with the 20 year old rule but really,do you consider a 1985 Olds Cutlass an 'antique' automobile? As for the issue of an age cutoff for 'regular' antiques i've been dealing in antiques for almost 30 years and trust me, the general consensus among MOST in the business is 100 years. It's obviously not a written rule, but that is the cutoff for considering it an 'official' antique. I get a kick everytime I talk to someone at a flea market or auction who tells me "yea, i've got an antique washer machine from the 30's, or I have a antique TV from the 50's. The word antique is used by many for anything 'old', and that's a shame. Hope this helps.
Steve