SIRIUS: I haven't a clue who put your name in that goblet, Harry, but whoever did is no friend to you. People die in this tournament.
HARRY: I'm not ready for this, Sirius.
SIRIUS: You don't have a choice.
Harry's about to grow up real quick. He's being forced to compete in the Triwizard Tournament, even though he's not technically old enough—but apparently, if the Goblet of Fire spews out your name, you have to honor its decision. His wizarding skills are probably well behind the older students', but he'll just have to do the best he can.
MCGONAGALL: What? Do nothing? Offer him up as bait? Potter is a boy, not a piece of meat.
Professor McGonagall is horrified that they are going to send a kid into this competition. Apparently, to her, it's like sacrificing him or, to use her words, treating him like "meat." Not exactly feeling great about Harry's prospects for winning.
HARRY: I was just wondering if maybe you wanted to go to the ball with me.
CHO: Oh, um, Harry, I'm sorry, but someone's already asked me. And…well, I've said I'll go with him.
HARRY: Okay. Yeah. Great. Fine. No problem. Okay. Good.
CHO: Harry? I really am sorry.
Aww, so sweet—Harry likes a girl. The downside: she's already agreed to go to he dance with someone else. The upside: she is clearly disappointed that she now doesn't get to go with Harry. So, it looks like she likes him, too. Guess we'll have to stay tuned for more on that.
RON: Oi, Hermione. You're a girl.
HERMIONE: Very well spotted.
RON: Come with one of us? Come on. It's one thing for a bloke to show up alone.
For a girl, it's just sad.
HERMIONE: I won't be going alone, because, believe it or not, someone's asked me!
And l said yes.
Ron probably needs to work on his sweet talking skills if he wants to dive into the dating pool. As you might imagine, Hermione finds his invitation pretty insulting (to her and to all girls). And besides, she's already got a date. Hmm, wonder who that is?
HERMIONE: Actually, we don't really talk at all. Viktor's more of a physical being.
I just mean he's not particularly loquacious. Mostly, he watches me study. It's a bit annoying, actually.
Mystery solved: Hermione is dating Quidditch whiz Viktor Krum. She and Viktor apparently don't have the chattiest of relationships, but he likes to watch her study. Sounds, er, romantic?
HERMIONE: Next time there's a ball, pluck up the courage and ask me before somebody else does! And not as a last resort.
Hermione's livid at Ron because he's giving her a hard time about dating Krum. Her interpretation? He's just mad that Hermione wasn't free to go with him. He claims he has no idea what she's talking about, but it seems pretty clear: these two have a romance brewing.
DUMBLEDORE: Curiosity is not a sin, Harry, but you should exercise caution.
Dumbledore tells Harry this when he finds the boy looking into his "Pensieve," which is where he stashes his memories to avoid overloading his brain. This quote doesn't really have anything to do with coming of age per se, but he's dropping some solid adult advice here: as Harry's life gets more dangerous, he really should try not to take on too much too fast, even just in terms of knowledge.
CEDRIC: You know, for a moment there, I thought you were going to let it get me.
HARRY: For a moment, so did I.
CEDRIC: Some game, huh?
HARRY: Some game.
Stating the obvious here: the Triwizard Cup is not for kids. At this moment, Cedric and Harry are trying to find their way out of a maze that basically just tried to eat Cedric. Some game indeed.
HERMIONE: Everything's going to change now, isn't it?
They're probably mostly talking about the fact that Voldemort is back, but it goes for their personal lives, too: these kids aren't kids anymore, and their relationships are about to change a lot, too.