PY: He must simply grow up
Why dont you wake up to the world. This is something that all men have from age 10 to 100 (if not younger). It is not something that makes the man immature. It is something that god put in the world and it was put here for a very good reason (. In fact it was taken away but needed to be put back again). The reason woman have tznius is so they dont make it harder for the men to fight the urge. (No it was not put there because the girl is a bas yisroel who is like a princess and a princess is dignified.)
As for what is considered not tznius it all depends on your perspective. I went from being extremely religious to not religious at all in just 6 months and what i view now as not tznius is very diffrent than what i considered not tznius 6 months ago. (This is the same with every aspect of religion.) In fact what a girl I may have looked twice at I wouldnt even look at once now because she is dressed so tznius.