Well... I don't know as it's common to regress with your mental health the older you get. From what little bit I've read, people in their 50's tend to struggle with more depression. But then as people get into their 60's & beyond they tend to become happier & more content. (I don't know it that's either true or accurate. It's just what I seem to recall having read somewhere.) It's probably different for everyone I suspect.

That's not the way it has been for me. I managed to keep myself on an even keel so to speak, & keep all of my mental health issues hidden, until around the age of 50. Around that time I had a not all that serious (in the whole scheme of things) bout with cancer along with some related physical issues. And that ended up being the proverbial straw that broke the camel's back. So, as a result, I've been slowly unravelling ever since. (I still am.)

I have been able able to recover my ability to keep it all to myself over time. But every day I wonder how much longer I can manage to continue. Anxiety has become a major concern for me the older I've gotten. And my communications skills have gone down the tubes because I'm pretty-much a total recluse at this stage of my life. So while my experience doesn't make regressing as one gets older common, or "normal", that has certainly been the experience I've had.