Vintage and dated are two different things.
A piece of clothing becomes vintage when it's older than twenty years. Older than one hundred and it's considered to be antique.
Dated means not fashionable/on trend/in vogue, something obviously old-fashioned. It's even more nuanced than this, so things such as cut, fabric, collar, sleeve, length, pocket placement, even the colour can make something dated rather than current.
Even semantics matter. Calf-length and midi-length are actually they're the same thing, but the former is old-fashioned and evocative of 1930s and 40s fashion, whereas the latter is what the stores are selling now.
So, back to your original question. Is a twenty five year old outfit unfashionable or stylish. It completely depends what it is.