There is a lot of bull spoken about about this sort of thing especially by those who say stuff like 100# isn't much it's a starting weight.
I was young once and didn't need to warm up or any of that nonsense, but I'm older and wiser now... you can hurt yourself with a 40# bow on a cold day if you aren't warm.
Anyhow back to the question. Little and often is how to practice and you'll get there in a month assuming you are of reasonable build.
10 push ups night and morning bare minimum. And I mean proper full chest to the floor pushups, not little twitches. Elbows out wide as if in the bow. Slow on the up and the down, if you want to show off you can clap your hands when you hit the top of the up
Shoot at least 5 shots every day from the heaviest bow you can get that full warbow draw from to get the technique. Ideally have someone who can shoot 'em give you some pointers.
Remember not everyone can reach 32". My full draw under a load is about 31"...( with a tape measure I can draw 41"... which is meaningless).
One good exercise I found is lean backwards into an open doorway with your elbows out at shoulder level. Use your elbows to lever your body back and forth, slowly inch your feet further from the door way so you are leaning back more. Obviously don't fall over backwards and smash your skull.
The beauty of this exercise is you can do it almost anywhere (if you don't mind looking daft).
Do pull ups on anything you can.
Good one for the shoulders is link your fingers and imagine you have a tennis ball in your palms and roll it round the back of your head in both directions.
Even sitting at a desk you can link hands and pull 'em against each other. I once work with a guy who was into isometrics. If he was carrying an empty cardboard box he'd tense up and strain as if it was an anvil he was carrying
Like I said, little and often.
When you do try for it, warm up first on lighter bows, video yourself so you can see what you are doing.
Last thing... a bow is much easier to draw when there's an arrow* nocked (doubtless it's just psychological) but make some arrows with nocks that click onto the string nicely so that you are not worried about keeping the arrow on the string.
Don't try the heavy bow until you can get it to say 28 or more... If you try to pull a bow that's waaay too heavy you won't get far enough to use the leverage and physics... it will just be a brute force straight pull and that's the hard bit.(Like Ian said)
Don't forget to breathe in to expand the chest (some people will say breathe out) and draw up wiping your forehead with the right hand and then heaving that right elbow down and back.
Know you can do it...
It's a balance of muscle, technique, will power and a pinch of stupidity
Something like 85#@32" would be a good intermediate to practice on.
Just out of interest, your 65#@30 is prob about 35# at 19" where the 100# @ 32" would be about 50# @19"
That shows the importance of draw length... you can obviously pull more than 50#, but not when your shoulders are not coming into play which is what Ian was saying.
Del
* Drawing without an arrow is BAD, because the let down is prob more strain than the draw, much better to loose.