I made a guess at 15+ years, but it could have been 20 or more. I never did know how old he was for sure. I dated a professor I had in college (after I finished two of his courses, I wasn't legally "his student" anymore) and he was around 20 or so years older than I was. It didn't last long. I was in my late teens and simply wasn't mature enough for him. He had a PhD (two actually) and a house, and bills to pay, and a full time job and was writing a book, and doing research, and all I did was my college work, a part time job for some money and PARTY! (OK, I had one research project in the works, but it was diddly compared to the very seriously taken, peer reviewed published work he did regularly.) He said I had enough brains for him, but not enough intent. Whatever that meant.
My Man is a bit older than I am, but not as old as this man was. Now that I think about it, now, this other man would be in his 60s! It never occurred to me before......