Marketing is part of any sale. OP should try to get the most money he can for his bass(es). If the word "vintage" adds value for some, he should use it (if he thinks it applies). Rarely would the word "vintage" ever turn off a potential buyer who is really interested in the bass. Sure, it will offend boomers who think anything manufactured after their 18th birthday is garbage. But they likely wouldn't be interested in a "vintage" instrument from after that period anyway. So they don't count.
In other words, let's just say I'm very interested in a 1995 Fender Roscoe Beck Signature bass. The seller uses the 25 year mark as a parameter to go ahead and describe his bass as "vintage". I frankly don't care. If I want the bass, that word won't turn me off. Anyone who IS turned off by that, likely wouldn't buy the bass anyway. Anyone who would otherwise buy that bass, but can't bring themselves to do it because the seller called it "vintage", has serious emotional/mental issues.