I wish your father was near me here in KY. Heck, he and I may even be near the same age.
I think a lot of us guys, especially old school have this concern of enough poundage. I had it for years with bows, firearms, vehicles, bass boats, etc. I guess it is a deep down, always wanting more and better thing.
I just had Mike Mecredy build a Maddog Prairie Predator for me and had to "MAKE" myself order a lower poundage bow because, much like your father, my subconscious wanted to order higher poundage.
BUT......I held my nose, closed my eys, and had Mike build the bow in #41 at 28" and I draw about 27"-27.5".
If your father could shoot this bow and see what a "Thwack" the arrows have a 20 yards, he would have zero concerns about the killing ability of a bow in this poundage range.
Please feel free to have him contact me personally if I may help in any way. He and I can discuss archery "AND" shoulder issues.