Old person here as well.
The trick for me was making sure not to jump at the edge of a platform or whatever else I was jumping from. The higher the DEX the further and higher you can jump so jump from the middle of the platforms. It helps sometimes also to have your char walk rather than run on some of the jumps to soften (lessen) the jump.
If it possible (it is in the Barbatos quest), the last jump down after all the tedious jumping you can just press U go back to the Battle Tower and wing it back to the ent - damn that last jump.
And a whole lot of spamming Quicksave!
It took me a good 15 - 20 minutes the first go rounds because I was becoming frustrated, but now that I have already done it and playing other char's it isn't so bad. Be patient with yourself =)
