Being 18, would this be your first car if you purchased one? If so, I'd highly recommend purchasing one that is currently on the road or close to roadworthy condition because owning your first car with a fresh licence and NOT being able to drive it, that's going to drive you insane and you'll either want to get the car quickly on the road to drive it (unlikely due to lack of funds) or sell it off.
If however this is in fact a second (or third, fourth, fifth, etc) car, I'd recommend giving it a crack at restoring one.
I bought my 240 when I was 22 (only just turned 23) and I had a heap of people saying, 'it's going to be hard', 'you're going to end up selling it off unfinished', rah rah rah, but you only use that as motivation to get it done quicker to prove them wrong
Being a uni student, my income isn't as big as some peoples and so therefore I'm not doing a massive restoration where every nut and bolt is replaced, but more a 'get it up to roadworthy condition' standard first and then possibly pulling it off the road down the track once I've had the chance to enjoy her.
I don't know your current situation mate but if you want it that bad, just do it. You'll soon find out whether it was the right decision or not. If it goes wrong, learn to think things through better next time
Good luck.