It’s not the age, it’s the mileage.
I’ll be 63 in a couple months and although I may sometimes refer to myself as old I don’t consider myself old. Old is when you can’t do normal everyday activities without a great deal of effort or pain.
I will be 49 in about a month. I don’t feel “old.” I have more energy now that I had a few years ago due to the fact that I lost the equivalent of two 22lb turkeys in fat. The extra weight was dragging me down in every way - physically and emotionally. My knees don’t hurt anymore and I can jog without feeling like my heart is going to burst. I had reached maximum density for sure and back then I did feel old, not to mention misearable. The other day I hopped from rock to rock (huge boulders, really) to the end of a very long jetty on the OR coast. I felt like a teenager.
I’m 60. I don’t FEEL ‘old’ inside, but I’m starting to look it, and I don’t have the energy or stamina I used to (not that I was ever an energetic live wire!). Going out in the evening sounds unappealing. I am slowing down. I take care walking down the stairs. A long day of shopping or a long walk and I really feel beat the next day. On the other hand, I still like lively music, still like fashion and putting on makeup, and enjoy most of the same interests I’ve always had. Only not so often. The most alarming thing is how FAST time goes by now, I’ll see a movie on TV and think, that movie is 10 years old. Where did those 10 years go??
I feel as though I just slipped under the wire-- turning 66 this week, so technically, I still fit into the 61-65 group. I don’t feel old. I’m looking older maybe, but I feel a lot freer now than I did when I was younger.
I’ve decided that I’d rather be a batty old broad than be a nice old lady and that yellow shoes go with everything.
Don’t forget you’re already in your next birthday year, since that day represents the entire year of whatever full-year age you will be then. 
Everyone would be a lot younger if we could only live on Neptune or Pluto.
No.
I’m 50 and in decent shape. I’m within my ideal BMI and still feel pretty good. I think I’m starting to experience some arthritis in my knuckles, but all-in-all I don’t feel any different than I did, say, 20 years ago.
I don’t dye my hair either! 
41, and like Jimmy Buffet, I’m growing older, but not up.
See, that seems a very strange definition to me. To me, old means you have reached a certain age. It has nothing to do with health or appearance. Someone can be 70, look like 50, and run marathons, but they are still old because they were born 70 years ago.
In fantasy books there are lots of “people” that may look young, but they are old because they have been around for a long time.
Seventy years ago that was said of people who were 60 or even younger.
To you, someone who’s 70 is old. To someone of 95, 70 is young, especially if running marathons. Age, at least to a certain extent, is in your mind.
And, it looks like the Nays have it! <gavel smash>
Congratulations.
Nine years ago I was 49, and considered myself old - but that was because I was in the Navy and for a good bit of the previous ten years I’d been, if not the oldest person around, then certainly one of the top two or three. (I was older than my last four skippers, for instance.)
One of the strangest things about retiring from the Navy and going to work as a civilian was being around people who were 20 or more years older than I. So now I’m 58 and I don’t consider myself old.
I’ll be 67 next week, and finally accept that I’m middle-aged. Old? Not yet.
While I don’t really consider myself old, I’m getting there, and I certainly don’t consider myself young. Somewhere in the middle.
46-50 and no, I don’t feel old. Until I hear my knees cracking.
I’m 51, and my age in my head is late 30s.
My age as measured by my arthritis is roughly 70.
Old is always at least five years older than me. I am 75.
I had no idea. You don’t sound that old. 
I’m still trying to come to terms that I’m turning 40 next month and a quarter of my life is over.
Or maybe they are an Olympic gymnast?
Feeling “old” is relative. If you are the 27 year old super-senior still hanging around the freshmen dorms, yeah, you should feel “old”. OTOH, you probably won’t feel old as the 27 year old associate at your law firm.
I understand what you are saying, but to me it just looks like denial. It’s like everyone thinks they are an above average driver.
When I get 70, yea, I’ll be old. I could be spry, I could be awesome, I could be hot, but if I look at the world objectively, I’ll be old.
But whatever floats your boat.