Alpine skiing.
I started at 15, and it was a frustrating struggle for a few years, learning the sport, as I could only afford wooden skis with screwed on edges. Then I scraped together enough money from my summer job to buy a new pair of Heads, and within a few months I was doing linked parallel turns. Got instructor and ski patrol certifications later, and at 66, I'm still enjoying the sport.
Nowadays, I need a break every two hours or so, when the quads start hurting

, but parabolic skis really cut down the effort.
It has cost a lot of dough over the years, but you pay as you go, and I'd do it all over again.