I have seen many project managers who are in their 50s and their 60s. I don't think project management, as a profession, imposes a maximum age on the individual, as the job is typically not (physical) labor intensive, so anyone who doesn't have any health issues can still do the job, regardless of the age.
Project managers can retire whenever they want, and I think a project manager who's healthy enough can manage a project while he is in his 70s even better than a project manager who is in his early 30s (I'm saying better because he will have much more experience than the younger PM).
I say go ahead with project management if you're planning your "very long term career path". It's the right way to go, and again, you only retire whenever you want, as long as you can do your job...