Just introduce him to this site.
Man,I feel your pain,I live that realityeveryday.My family doesn't understand or WANT TO the differences in what a bow that fits you and one that doesn't means.
My stepdadgave my 14 year old nephew (that he can't shoot anymore due to tendonitous) his bow.A 70# Mathews Z light with a 30" draw.My nephew can only pull about 60# on a good day and has about a 27" draw length.
I have tried to explain to both of them that it is a bad idea to even attemt this but they don't listen.
They both know my abilities as a shooter and tuner but it still falls on deaf ears.
My stepdad could easily still hunt with a compound but chooses not to because he can get a letter from a doctor that allows him to use a crossbow just because he can't use the 70# bow anymore.
My advice is to let it be and offer help when the time arrises.