As quite a few people have said, Facebook is generally mostly for the over 40s now. I have got around 90 people on my facebook, and around 40 of them are under 35... Work colleagues, ex work colleagues, my adult children, their friends in their 20s and any 30s, and my friends adult children.
I think I can count on the fingers of one hand the amount of posts that the under 35s have put on Facebook in the last two or three years. Over 40s seem to live on there, and yeah, as that amusing 3 line quote I quoted said - people on facebook want to tell you their life is not shit, indeed it is amazing. It's pretty much all over 40s who post a lot, and they all have great lives, and amazing, clever children, and a wonderful relationship with their spouse/partner. Every single thing they do is documented, from a costa with their mate, to seeing their amazing granny, or noo noo as the kids call her. 😆
As people have said on here, younger folk tend to use Instagram a lot more. As the previous poster said before me, I actually find Instagram really boring. It's just a load of pictures, and many are not of people... Just scenes and stuff... VERY few instagram accounts interest me. I only have one because a few young adults I know have it -including my DC, and I like to see their photos.
Instagram is full of fairly normal girls putting loads of filters on and tons of make up, making themselves look completely different... They thrive off the 'likes' and the 'favourites' and the positive comments, and their worst nightmare is people not noticing or commenting on - and liking their pics!
My daughter's fiancé has got a cousin who is on Instagram, and she looked like actually quite a pretty girl, but I was shocked when I saw her. She was actually 4 or 5 stone heavier than she looked on her pictures and quite plain. I know that sounds catty, but I'm just stating a fact. I don't know how she managed to do it. She looked like a different person.
But yeah, it doesn't really do you any favours making yourself look completely different and much, much better on your online photographs! 
I have a facebook account, but only post on it maybe once a month, and will often post a few photos.. I only look at it once or twice a week for a couple of minutes (to see if there's any messages from anyone...) CBA with seeing people fake and filtered lives to be honest. I keep facebook open as I have family and friends abroad, and it's a good, quick way to stay in touch, and contact people.
Only ever posted about a dozen pics on Instagram. In 3 years.