I agree. Lying in a sexual stituation is a no no, very harmful to a person, people have arguments in this stituation about who's in the wrong alot but let's be honest if you meet someone in a club for 21's which requires I.D to get, you will assume that everyone in thar club is 21 or over... I digress.
As for other things is does depend on mental maturity as well as life experience usually that does come with age, being around similar ages does grantee more relatability when it comes to life experience, however you can still can have other conversations with people who don't share that relatability but you have similar things in common. Friendships can still happen between ages gaps, altjough the longer the gap the less likely the friendship works and will have a different dynamic (I. E 20+ and much older 60+ person is fine they're both adults no issue, compared to 25 and 6 year old, different dynamic of friendship more like a baby sitter than a friend and considered quite strange)
Lying about your age, is somewhat unnecessary but I understand why people do. People as much as they try not to do judge by age and do invalidate a younger persons opinion especially if they have no real experience on the matter, and even if the did they are assumed not to know anything cause they're a child.
It happened to me alot as a child despite me going through alot of things that not even adults go through and doing things that adults should be doing (working taking care of kids etc)
After a while my mental maturity started showing through so now I'm just a old lady inside at 30 lol
However I have lied on old school website chats, never had a profile just used to log in at school with guest accounts during break when I was 13, lied said I was 15 or sometimes 18.... That lead to my first emailed dick pic
(it wasn't traumatising per say, I had multiple email accounts so I used one specifically for this... But the sheer size was shocking especially for a 13 year old who thought she was a lesbian at the time lol) but it was quite common to go on Web chats that we did, our whole year did it, my friend went deep, lied made herself to be someone she's not said she was 16, got a phone number, but because she couldnt talk cause her voice was less than desirable she got me to... I confessed to him he spoke to her said he liked me more he was only 15 not 18, I was turning 14, we talked for a bit, as friends even when I went to college it was weird, then we stopped, he got married, we both have kids and we still have each other on Facebook its strange.