I've been in the same boat for years, bought mine when I was 18. Drove it for a few years, got a better job and decided to build the car I wanted... I'm now about to turn 40, have a family, and the mustang is still waiting for re-assembly. In the process, I've put it up for sale multiple times, spent WAY more money then the car was worth, and I still enjoy the occasional bit of time I get to spend working on it. I just like to think about all of the people who wish they still had the car they were driving way back when.
Good luck on your project, but most of all enjoy it!
68 Mustang Coupe