I'm 44 and most of the interest comes from people in their 20s and people considerably older than me. It's weird, in my late 30s there was virtually zero interest - probably because when you post that you are 39 people assume you are really in your late 50s and using an old picture...but once I turned 40 there was a wave of daddy-chasers.
I experienced something similar as I gained weight, where when I had a decent amount of muscle but no abs, I was pretty damn invisible, but when I crossed the line from "a little overweight" to "fat" I entered a new sexual marketspace(and what was shocking to find is that there are ripped dudes into fat guys). I should probably start gathering data, as I am now embarking on a weight-loss program in anticipation of back surgery, and see how many hits I get at different weights....