A 5.0 Foxbody isn't fast by today's standards, but it has a lot of potential (a lot more than an economy hatchback). The kid could easily get it into the 13s if he's savvy about his pocket money and learning to wrench. Plus, it enables things like burnouts and donuts that aren't really on the table for a modern economy car.A 5.0 mustang isn't fast tho. It was fast AT THE TIME, but it's still a pretty slow car by today's standards. 15 second 1/4 miles, just looked it up. I personally don't see a huge difference between a 15 second car and a 17 second car... >shrug<
Let me explain it to you this way: I borrowed money and spent every dollar I had to buy my Charger when I was 16. It kept me busy fixing things, and I learned a lot. I also didn't drive it super hard, because I spent everything I had on it. Later when I was 17, I bought a used neon to use in the winter. It had 130hp, and I drove the PISS out of that car, at the limit, all the god damn time. I didn't care about it and drove it harder because of that. E brakes slides, street races, etc. Charger was a cruiser and fast but I didn't want to hurt it since I loved the thing.
As to whether the kid will hoon it... that depends somewhat on the kid. My biggest reservation would be lack of airbags and other safety equipment if they do end up binning it (due to either bad choices or inexperience). There's has to be some cars from the late 90s or early 00s that can provide a similar experience with much better safety.