Transport Enthusiasts - pretty common really.
OK I think it is time to clear up some of the points about spotting ect.
As you can see all of the "spotting" involves transport. "Spotting" is a sub set of being a transport enthusiast.
I like transport and machines, I can appreciate a vintage bus, an E Type Jaguar, an old Bedford coach, a Vulcan, a Deltic, a 9F, or a nice narrow boat.
(This can sort of apply to the gadget fans and computer builders - lots of shiny bits)
This is normal for most men and some women. The person spotting a bus back then may now be a manager or may run his own preserved bus. The 1970s to 1980s train spotters and photographers probably own 3/4s or so of all the preserved "Modern" traction (assuming modern as post 1950), just as the 1950s-60s steam spotters bought up the contents of Woodhams scrap yard.
The sad lonely ones though let it go to obsession, I have seen a few and they were not heroes or anything, they were generally pitied, some were well known and TBH were treated as a bit of a joke.
Most of the spotters I would say were teenage to early twenties and there were a few girls with their boy friends.
Almost all have gone now to railway preservation if at all interested now due to the loss of many favourite locomotives.
The funniest thing is that within spotter circles there were factions - support you favourite loco class - now they were funny!
BTW I am a transport and machine enthusiast.