I'm 42.
Been driving GTIs on and off since I was 18.
All bought out of my own pocket, no company cars etc BUT never bought a brand new one. Some were newish ones and some were older ones.
GTIs are bought by people of all ages as they are all rounders. They're sporty-ish but still grown up and aren't out and out track cars like some of the harder riding peaky hot hatches out there.
Some people will buy them for their iconic image, some because they are Golfs pure and simple, some because they want a sports car that doesn't rattle their teeth, some because they know they can modify them to become truly great drivers cars yet are still low key and socially acceptable and some simply because they have a VW badge and they are too up their own arses to buy a SEAT or Skoda!!

So you'll have rich kids who's parents are buying them as they are iconic but have a good reputation for safety.
Company car drivers who don't want a 'normal' looking hatchback.
Older people who have a bit of savings and are young at heart.
And people like me who grew up and grew old with the things.
So you will see a massive range of ages of GTI driver, that's why they are a best seller and have been for so very long.........

And the same goes for GTDs, only I'll credit these preople with a little more financial sense or a stricter company car scheme!!!
