I suspect for all of that it is DNA that has by far the largest impact.
My father died at 92, and mainly due to fairly serious residual injuries from WW2. He was overweight, had high blood pressure, worried constantly about everything, highly stressed. But he otherwise led a healthy and active life.
My mother is currently 93 and shows no serious signs of slowing down anytime soon. Her memory and ability to remember appears better than mine, and her mind is still relatively sharp. She still lives alone and supports herself.
All of this bodes well for my potential for longevity whether I meditate or not. And now that Maharishi has died so young I don't see too much point in it as a regular activity. The Sidhi program was always much too long to do twice per day anyway.
I'd estimate that the factors that contribute to longevity would be something like this -
DNA 96%
Food, drink, and environment 2%
Healthy active lifestyle 1.9%
Meditation 0.1%
The only real value for TM is when I do feel really stressed about something I can go sit anywhere for a few mins and disolve the issue entirely, and very fast.