The concept of "getting old" can be very subjective. Some people start calling themselves old when they're still technically young, because the mere feeling of being a full-grown adult feels innately "old" compared to the play of childhood and adolescence.
Other people save the term "old" for when they're facing retirement, legally considered a senior, or generally older than most people they meet. And still, some people eschew the concept of being old altogether, since it's so often used as a way to discount oneself or claim irrelevance.
Regardless of the ways you define it, there's one thing most of us can agree on: getting older is a trip. There are moments when you remember something from the past and realize just how many years ago it occurred and it sends you into a tailspin. In other moments, it's deeply comforting to recall just how much you've lived through, and take comfort that you can live through more.