It really all depends what you want to do in the aviation world. If you are happy pottering about as an instructor earning pretty much nothing, then I suspect you could start any time in your 30s or 40s and enjoy 152s and the the like till the eyes pack up
If you have you heart set on flying heavies for a major, then you'd had better have thought about building the hours on multi-engines during your mid-20s, with some sort of degree going in as a help.
Generally, speaking, in your late 30s with a hundred hours of single engine pottering around will exclude you from the majors as competition remains tough and there are plenty good candidates in and out the country with Canadian quals to choose from...