When I graduated high school I was a 140 pound bag of bones. I hit the growth spurt in college all the good athletes in my high school hit when they were about 14. When I graduated college, I was a hair short of 6' and about 185, I felt I was at my athletic peak balancing strength, speed, and flexibility. At that time I was working out a lot, mostly eating decent, and drinking a crap ton of beer. Not sure how reliable it was but I remember doing a body fat thing at work and was 15%. I wouldn't want to have been much thinner that that so I'd say that was my ideal. I'm at 200 now, and I still feel decent but can't imagine putting on another 10 pounds. I may be a bit more of an immovable object but I've definitely lost a step and some flexibility. I have some dad strength now but would imagine most of that 15 pounds I put on is lard. So just by extrapolating that I have to be sitting about 20% now. Wouldn't mind getting back to 15% if I ever find the time to workout again.