Manburg,
Actually what got me started is Panerai. I like the watch and brand and learnt a little about the history of the brand and its military links. I was told that even our Naval Officers in Malaysia were issued Panerai watches. They do have to return the watches once they leave the service. Don't what rank you have to be though.
The other reason is the industry I was in, aviation. So I started to read about pilot or aviator watches. Had a look at German issued watches and how readable the watches were. I even built a couple with the A and B dials. After that it was Stowa, LACO and finally IWC mk. XV. Found out about American issued Hamilton in the GG-W-113 and also the British issued Precista and CWC. All pretty affordable. I had the full set, covering Army to Navy, Marines to RAF. Only the RAF and 1 Army (Fat Case) remains. The rest have found good homes.
I even started looking at aviation related watches. Hence if you look at my collection, most of the watches have some links to the aviation industry.
As for what qualifies as vintage, I was told anything 25 years old and above is considered vintage.