Well I'm 19 and got made redundant so I had to sell my VR6 Highline (yes, I was very gutted) and I now have to put up with a 1.6 cl Mk3 (see sig).
It's done 190,000 miles (yes you read that correct) and it's still bulletproof. In fact, I'd say it's only just broken in!
For a heavy car with a small engine, it sure as hell gets from 0-100mph quick (at Santa Pod of course), with a top speed of 120mph. Ok not supercar speeds but where do you get to do above 70 on public roads?
And I raced a Saxo VTR last Friday, from 0-40mph, and I won by about 2-3ft. Yes I know 2-3ft isn't a lot, but considering the Saxo has 25bhp more than my car and probably weighs half of what my car weighs, I thought that was pretty good going.
A decent coilover kit and some good tyres should see you keeping up with GTI's on the twisties (as I found out yesterday evening

)
I used to do an average of 250 miles on a Saturday night with absolutely no problems. And in the year of owning my car I've only had to replace a cv joint and a starter motor, pretty good huh

So to be honest if you choose a good one, or you look after the car you choose, it'll last forever!
The only BAD thing I have to say about Mk3's is they like rust. My car is solid underneath but the drivers side rear wheel arch and the bottom of the drivers door had seen better days when I bought the car.. I've temporarily repaired them.. saving for a full respray, but you can't expect it to be showroom condition when it has had 14 years of abuse from our crappy roads.