I'm with @Sandy_Hancock in that I consider "vintage" to be fully manual glass.
While we can wax poetic about the charms of "vintage" or "pre-AF" glass, a very practical aspect is the possibility of saving money vs buying digital-era lenses, and also being able to experience more exotically-specified lenses than is readily available in K-mount.
An example of the former: rather than spending $1500-2000 on the DFA 150-450, I bought the
A 400/5.6 for a fraction of the price. The A400 is a good sharp lens, not too large & heavy and a pleasure to use. The only significant flaw is noticeable CA unless stopped down.
An example of the latter: I have the
Tamron Adaptall 300/2.8 (360B),
400/4 (65B) and
Pentax K 500/4.5... lenses whose specifications are not readily available in K-mount, and despite not being as convenient to use and not as optically "perfect" as modern lenses they are very good and can produce images with a certain "look" that is associated with expensive, high-end glass... at a total cost no more than a used DFA 150-450.