Hands Free Masturbation

At age 17 I could masturbate just by thinking about cumming. I would go to a quiet area in the countryside, strip and think about girls and fucking. The more I thought, the harder I became, and then after a while I would cum. Not a lot, so I had to follow up with a hand job. 

I could no longer do that at age 20 so it probably was a time of peak testosterone. 

Have others had the same expereince ?