I'm 66, but only on HRT for 4 years.
At 60, I was just playing out the string - a suicide by neglect. Now I'm lighter, more fit, and my health has done a total turnaround.
Any way I look at it, HRT has given me 4 extra years already and no reason to expect anything to change soon.
As just a general comment, it doesn't seem to matter how many years you have, but how you use the years that you're granted.