Is this ok for an 9 yr old to see
I'm interested to see what some parents say, but it's something I thought about while watching it. I don't have kids of my own but I definitely got the sense that it's almost more kid friendly than the first, especially with a lot of the jokes and gags being slapstick, but it also features main characters who are a bit of jerks and abrasive to even their friends so while I don't think there is too much cursing, and nothing that I remember as being as risque as the Jackson Pollack painting joke from the first which was more implied and let your mind fill in the blanks, it's Gunn's same sense of humor that's​ crude without being obscene (making lots of sex jokes that push the boundaries) but it's the sort of writing that makes it dirtier for adults than kids. Even some of the cursing is like the first where they call people "a-holes" or Rocket says "he says welcome to the fricken GotG, but he didn't use fricken".
Without seeing it again, I'd give it a "hard PG-13" in the same way people talk about a "hard R" film, but I think 9 is about the age most parents might feel comfortable taking their kids because even some scene get a little too intense for much younger kids, but I think people's mileage my vary.
I remember parents taking very young kids to the first film, more than I tend to see for most Marvel films these days, and I wondered if the film was aimed too old for them but I expect this to have a similar spread of older audience for the music, younger for Rocket and Groot, and an immature, adolescent sense of humor and 80's references that pleases everyone in-between. It's almost like a throwback PG kid's movie from the 80s but with less cursing and less nudity (in other words, none) than they allowed back then, which seems pretty edgy these days to consider this a kid friendly movie but it kind of is.
The violence also firmly places it in the PG 13 realm, to me, but that also skirts the rating board a bit since the body count is huge in one scene with Yondu, but it's mainly all an arrow quickly flying through people, then they also fight unmanned ships where no one dies. There is alien violence that also gets a pass since alien blood is okay and there are moments at the end fighting Ego that get a little gruesome, but only in an odd, uncomfortable way because, he's not a physical being but a cosmic entity that can rebuild himself. Again, it's the sort of thing that makes it a hard PG 13 these days, but it is possibly less gory and violent than some PG films in the 80s.
Honestly I think more younger kids will like this than Civil War or BvS, for instance, which both got way more serious in tone. Like how people here are clowning the Taserface gag, I can see a 9 year old either thinking it's funny or dumb, where most adults wouldn't find it funny, but a 6 year old would love it. It might be the funniest joke to a 6 year old besides the slapstick.