That depends, first swung a club in our garden when I was about 5, then I was probably around 10-11 when I first started playing quite a bit with my dad, but then I stopped playing and didn't start playing again until my late 20's for a few years playing with friends from work before a restructure saw us all move locations and even jobs in some cases
If you are talking about when I took it more seriously, I would say it is about 8-9 years ago, but definitely more so in the last 4-5 years
I had a group lesson about age 11-13. I played a few times over a couple of years. I liked it but didn't have friends who golfed or course access. Then no golf until a "work" round in my late 40's. My wife surprised me with a golf lesson on a HI trip in Jan 2015. Loved it. Took up golf as a passion-fueled activity formally at 52 51 (math!), which is in my mind when I started playing golf.
I started when I was around 12. My father took up the game then and I tagged along. He didn't take to it and quit after awhile but I kept on. That was 49 years ago.
Started when I was 15, then had a break of 3 years from the ages of 19-22, played off and on from 22-30 and now for the last 9 years have played very regularly.
I went out with buddies and played occasionally in high school. We were never serious. Played off and on through my 20s but really started caring and trying around 30.
15 or 16 when my mates and I would go hack around a local to get rid of the hangover.
Started taking it seriously when in my early 20's and joined the local club, bought a real set of clubs (King Cobra) and first round out with them broke 100.
I started swinging before I was old enough to play organized sports. Started getting out on the course around 8 or 9. Really tried to get better over the summer while I was in college. Started working and golf took a backseat until I turned 30 last year.