Well, personally, I take it as an insult. Vintage wine is typically older than the standard stuff in the box that I drink. To say someone is like vintage wine might suggest they have aged well, look good for their age, are polished in their behaviour, etc., but to me, it reminds me of a birthday card I got my mother-in-law:
"Women are like a fine wine. They get better with age," it said on the front.
So I added, "So you must be really good now!"