Just to throw my bit into this.
At 66 I knew nothing about sailing, had never hauled a halyard (didn't know what one was). Only experience was steering a friend's boat for a short while a few years earlier.
But I was keen, so bought a 34ft sloop, cruiser-racer, and taught myself with a bit of advice (I didn't want assistance) from friends, reading, and forums such as this.
I love it and am getting more adept all the time. Have Sandra as crew but she knows even less than I knew. Longest single expedition so far has been 240miles, but have plans for much more.
In my view it's a matter of enthusiasm, time, mental outlook and (if you're lucky - I am) physical condition (as we all know some money can help too) and not much at all to do with age as such.
If you're keen then go to it. Sailing is really great!!