I can see both points of view, and I think they're both valid.
I do think it's a problem that our fan base is so old. I often look around me at all the silver-haired and grey heads (myself included) — all of us were 14 on the Kippax once upon a time — and worry, “Where is the younger generation that should be replacing us?” And I have a horrible feeling that they will never come. Why? Because society itself has changed so radically. A great many of us live through a computer or smart phone screen, very nearly 24/7, and think it's real life. Not only are the kids no exception to this, they are the ones who have grown up knowing nothing else. For them, it is real life. What's the difference for them between being at the Etihad, and watching the streamed match at home? They've got to get off their arses (or their parents have got to get off their arses) for the former, pay a fair whack to get in (read — parents etc.) and hang around in the pissing rain waiting twenty minutes to half an hour to get on a tram to Ashton or Piccadilly at the end of it. Just easier to watch it at home on Sky or an illegal stream, or watch the highlights on MOTD later on.
It is a problem, and one that's much larger than the simple question of MCFC.
On the other hand, I suspect the second poster is totally right. It's the parents (some of them) thinking that their little Johnny has the right to do what the f— he likes because they're at the match and they've paid.
I don't think anyone should invade the pitch, ever, except on the occasions when Sergio Aguero scores a title-winning goal in the 93rd minute of the final match of the season, healing 44 years of hurt.
(That said, I've got a vague memory of jumping over the wall at the bottom of the Kippax, along with several hundred other kids, to go for a little stroll on the turf at the end of an absolutely meaningless season-ending match against, I think, Sunderland in about 1970. There was no-one around to give me a clip around the earhole for it…;-) No pesky stewards at the time, and the coppers were completely overrun )