I know that at your age, anything over 35 or 40 appears a fossil....but I have friends (pretty active people, too!) who are 80 plus (last week my friend's 90 year old father sang so well at our get-together, and cracked a few wicked jokes as well!) so I don't think of myself as "old".
I think some of my mental perception of being "mature" rather than "old" also has to do with the fact that I am in good health and pretty fit....and since I love learning new stuff, I don't think I have entered old age just yet. The bad part about my age is that I know that definitely, more than half my life is over, and I have so little time to learn more...but the plus is, I am now so comfortable in my own identity, I don't worry about stuff like external appearances--whether mine or others--, and can enjoy a life of more leisure than earlier.
In face-to-face relationships, too, I have been lucky to be able to have friends who are 30 or 35 years younger, and 30 or 35 years older, than I am...it's so nice to interact with people of all ages!