gayinterest saidAge is irrelevant. It's how you live your life that is important.
I wouldn't go quite as far as the first sentence but do agree with the last
35 is certainly not old but it is about the time we begin to realize we aren't immortal, that we are 'aging'. In many ways, I regard the 20 year span between 35 and 55 as 'the golden years'. The trials and tribulations of youth are behind us. We've 'found ourselves' for the most part. We may still go through 'mid life crises' of various sorts but we know how to deal with them.
For me the 10 year span from 55 to 65 have been very interesting. I've changed in ways I didn't anticipate. I've discovered that beyond a certain point, I can't control life. It happens. But over all I've become less stressed, more easy going, in some ways happier than I've ever been. I don't *feel* "old" (although I certainly look it). I truly *get* it that from here on my health has a LOT to do with how I live: What I eat, my activity level, what I think about, what I choose to do with the time I have left.
All that said, there are many things I know now that I wish I'd known decades ago.