"Too much" ...
"Too much" is how much people get involved and judgemental into other people's lives on this.
It used to be that friends would "warn" their friends about the number of disconnections in art, conversation, culture, etc... that people of greatly varying ages would discover about each other. But now days, people are just so fucking judgemental to a chronic fault, driven by media (in the US) which thrives on advertising (in the US), which thrives on ratings, which thrives on conflict.
It has been in my experience that people want to look at others and judge others so they will feel better about themselves. I don't have any vices (never drank, smoked, done drugs, etc...), been with the same woman and never think of leaving her ... ever ... and people will still try to find some way to guilt me -- the most common being, "you're rich" (even though my wife and I live much poorer than any of our colleagues, except my best friend and my wife's best friend).
When I was 18-19, I dated some 30 and early 40 somethings. Was it "right"? I don't give a fuck. Did some of them "take advantage of me"? Well, I was naive in some cases, but was that really, "taking advantage of me?" It's all a life experience.
We have the age of adulthood of 18 here in the US (ironically enough 21 for drinking in the US, which is stupid given the number of 18-20 year olds that binge drink, but that's another story). At age 18, you're legal. Do people stop acting naive and stupid at age 18? No. Maybe my wife was the only one who was well matured by 16-17 in her personal responsibility, but I'm sure I wasn't completely by 18. But 18 is where people must "draw the line," and it's good to have a line of minority v. majority. Beyond that, fuck everyone else.
The reality is that people should tell everyone else to fuck off when it comes to who they see and why. If people are down on them, don't let them get to you. Do not question yourself when others say something. Just go with it as long as it feels good and you are compatible. Even people of the same or similar ages don't always have the same experiences, so that's hardly different than age differences.
Hell, my wife and I are only 2 years different, and we can find plenty of experiences where we differ greatly, and have very complementary insides and views. Coincidentally that has made us more compatible, not less. I like egg whites, she likes egg yolks. That explains us well. We differ in our likes and desires, and yet, they seem so compatible at times. She's aggressive, I'm passive. She passionate, I'm conflict avoiding (yes, I really am -- it makes me one hell of a consultant).
Age differences? Enjoy them. Ignore everyone else, as long as you get alone. In fact, don't let age be the "excuse" in an argument. Make that rule #1. There's always something else at work that some basic attribute that people like to point out -- age, race, financial background, privilege, etc... Fuck everyone who tells you otherwise, honestly. Don't question it.