I used to masturbate as young as about 7, thinking about naked girls my age, or older. I didn't ejaculate, of course, but there would be a definite orgasmic sensation. I guess I stopped doing it regularly about a year later. I really rediscovered it around 11 when I snuck a peek at my older (adult) brother's Playboys and Penthouses while he was out. As soon as I saw those naked women spread for me I got super hard and soon had my first real orgasm with ejaculation. Damn that felt good. A few minutes later I had to do it all over again.
First orgasm with someone else? 17. An older woman.
Most orgasms with someone else in a single session? Seven, when I was 23 with a (different) older woman. That was a wild night. To my credit I backed up the next day and fucked her five more times. I was pretty sore after that. So was she.
I've met a few women who generally can only make themselves cum. One friend of mine had only ever been able to get herself off through masturbation, until she met me. She was 38 the first time she had an orgasm with another person (me). In the end she came five times that day (I only managed to cum four times myself).