I'm frugal, I save about 35-40% of my paycheck. I'm also in the 90th percentile of income, but given the fact that I live in a developing country, that just puts me in the middle class.
I think I could "semi retire" at 45 if I wanted. By "semi retire" I mean working 20 hours a week.
If I wanted to fully retire right now, I would need $720,000. I would put that in a fixed deposit at 5% and I would take half the returns to live off. That way, I would fight off inflation. Yes, $1500 a month is enough to have a more than decent lifestyle in a low income country, but if you want to be upper class, double those numbers.
I will probably never fully retire. I enjoy working, and not doing something productive would destroy my ego.