I don't consider myself old yet. I am only 55 and going on 56 in a couple of months. I remember when I was 25 - 30 I was really worried about what it would feel like if I made it to 50. Now at 55 I feel like I am in the best shape of my life both physically and mentally. There are 4 things that I prioritize in my life:

No - 1 Regular strength training
No - 2 Riding my bike which is both a hobby, pleasure and exercise at the same time
No - 3 Following a good diet
No - 4 Having a daily challenge of some sort. Lucky for me I have a job that's physically challenging and keeps me sharp and focused.