I think it's good that the hp's are mentioning Pnd to you tbh. I had no idea about it with my first (was 20) and the first I ever heard about it was at the 6 week check when the HV did a questionaire ( I totally lied).
I think I did have a touch of it with my first, and had a bad case of it after my second, by which time I was more clued up and asked for help.
I also agree with Mummytubb, the baby blues can hit any time in the first week, for me they hit pretty quickly. With my first they hit after 48 hours and lasted a couple of days (understandable as baby was in scbu, but released healthy after 48 hours).
With my second, about 24 hours after giving birth I just sobbed for hours, I have never sobbed like it, I couldn't breathe, I had nothing to cry about either.
But in both cases I just snapped out of it and was fine (for a few weeks, pnd kicked in later).
Baby blues can be pretty intense, but you may not even get them, I'm pretty sure there is no age correlation with pnd. It can happen to anyone regardless of circumstances.