When I got to 60 I thought if I don't pull 100# now I never will, so I trained up.
I was previously of reasonable natural fitness and could pull 70# @ 28" ok but not all day.
My day job was sedentary.
I started doing 10 push ups (slow and controlled) night and morning and also worked out an exercise leaning back into an open doorway with elbows extended using my chest and shoulders to lever myself back and forth ( I could do this at work now and then
... on the little and often principle of training). It only took me a few weeks (maybe 6?) to get up to the 100# at 32". The 32" was maybe a bit of a stretch (I think 30-31 is prob my natural warbow draw), but it meant I broke the 100# and 300yards
I think having a target archery background rather than a field/hunting background is a disadvantage as the classic target archer T draw is useless for heavy weights.
Having suitable manageable long draw bows helps get the technique (I made an 80# at 32" for practice)
You need some guidance from someone who actually shoots heavy bows... not someone who thinks they know about it... and at all costs avoid target archery "coaches" .
Del
PS listen to all advice but only take on that which makes sense and works for you.