Don't be depressed. It is an inevitable fact of life that we get older and one day we'll be proper old. It's disconcerting, but preferable to the alternative.
The people who are unhappy about getting old tend to be those who let things slip and didn't look after themselves. Whilst it's never too late to change one's lifestyle, there is no denying the fact that doing so early will bring bigger rewards.
Eating a healthy Mediterranean style diet, being active in all sorts of ways, exercising, having lots of interests and hobbies, nurturing relationships - as opposed to drifting along, eating crap food, drinking too much alcohol, spending too much time sitting in front of the telly.
I'm 70. I work out, walk a lot, watch what I eat but what I eat is delicious, I meet up with friends most days, still married to the guy I met at uni, spend time with my granddaughter, have a second career as an artist, tend to our garden, travel, ski, cycle, swim, go to the theatre, ballet, opera, exhibitions..... etc etc - there aren't enough hours in the day.
We don't know what life will throw at us, and I don't know how many years I have left - but while I'm healthy and have my marbles I keep on keeping on.