I think it's perfect.
I assume this is your son's first car. If it runs, drives, and the price is right, then it's the correct vehicle to buy. It will likely be used as basic transportation, treated less than ideally, probably accumulate some parking lot-type bumps and bruises, and PT Cruiser or not, won't be worth anything when he wants to replace it.
As far as longevity, it really shouldn't be a concern. How many kids put more than a few ten-thousand miles on their first car before replacing/upgrading? This isn't a long term decision where you should expect to get 20 years and 200k miles out of it.
Besides, if you're buying it for him, he has NOTHING to complain about. It's a free car.