Your first argument boils down to "it's difficult to leave so why bother". That's an objectively terrible reason to stay, no matter your political affiliation or feelings about the EU.
As far as the "old people did this to us" meme. The 75% of young people who purportedly are so strongly against brexit probably should have bothered to vote if they wanted that outcome.
Additionally, there are other factors than just age that correspond to voting outcome. E.g. degree education, having a passport, income level.
And if we afford those people a bit of empathy rather than casting them all as gullible fools or bad people, we might consider that they actually stand to benefit far less (or have plausible reasons to feel this way) from the EU than someone (such as the average HN reader) who has the privilege to e.g. be choosy about employment opportunities, be able to afford educating themselves, be able to afford to travel at will.
In any case there are many reasons to feel ambivalent about the EU. I do, and I've taken every opportunity that membership has afforded me. I still don't like how (or by whom) it is run or how expansive its powers have become over time.