My parents bought an old Renault and kept another one with the idea of restoring them. Never happened. But... I know someone else who did actually restore one

My parents bought an old Renault and kept another one with the idea of restoring them. Never happened. But... I know someone else who did actually restore one of those. And... I worked with a guy who restored a Porsche including rebuilding the engine, it used to sit in his office! (he was a mechanical engineer) and another guy (another engineer) who restored some old American car (forget the brand, maybe a Ford Crown Victoria?). Both these engineers had access to a fully equipped workshop and spent looong hours every day after work building and fixing parts. I used to do some work on my own car and motorcycles. It's hard work. There are a lot of enthusiasts who do this... I see them in old car shows. Not sure how many hire others to work on them...