I got my own 22 when I was 8. The first 4 or 5 years were not huge volumes, but what I could afford. I am now 68.
Picked berries in the summer, and other fruit in the fall, mainly to feed my 22.
Then, at 13, I got a part time job, and had more money.
I also discovered XELEX explosives [now Higginson's] and cheap 22 rimfire ammo by the case.

That is when I really started to shoot volumes of 22 ammo.
Also bought a Mossberg 151M semi-auto 22, which ate ammo at a much higher rate than did the old Single shot.
At present, I own 28 22 rimfires.
For several decades now, I have been in the habit of buying 2 or 3 cases at a time.
Surprising how quickly one can go through a case of ammo if you shoot a lot.
Short answer to the OP question....I really have no exact round count, but certainly approaching 400,000 rounds.
If I do not shoot 1000 rounds in a given month, I am disappointed. It's the least expensive way to practice.
Regards, Eagleye.