I know I've only been doing this for two terms now. So, compared to a lot of people, I don't have the experience or background. There's a lot of good advice/opinions here (I wish I would've read this before Wesley's first year!), and I was thinking, maybe, I could share something that hasn't been mentioned yet?
Personally, I think that what really makes RPGing realistic is character growth- emotionally, mentally, physically.
JK Rowling once said that she disliked stories where characters stayed children the whole way through- she wanted hers to experience growing up. And you need not look any farther than Neville for an example- his values remained the same, but he gained much of the confidence he was missing as a little first year.
So, for me, the thing I really want to see in Wesley is growth. Knowing more spells and being taller is a given, but I also want her, by her 7th year, to make it through Potions without puking or feeling like she's going to burst into tears about Lionfish hearts. And I definitely want her to grow out of fainting. I'm not saying I want her to loose her core beliefs, I just want her to mature. Because, when you think about it, students enter Hogwarts as children, and they leave it as adults, ready to enter the workforce.
I think, even if a character starts Hogwarts in their 7th year, they can still show growth. Every year brings new lessons, and those lessons can change the way they view the world, if only in a small way.
Of course, I know that there are exceptions- just like with every rule- some people don't grow up as much as others; some people might not grow up at all. Some people are ready for jobs at 17, some are even ready to get married, and others aren't. And that's okay. Variation, as others have stated before me, is what makes the world unique. I just think character growth is nice, even if it's something as small as growing 3 inches taller or learning a new spell.
Source:
Here's the JK Rowling quote I mentioned earlier:
"I always wanted Harry to grow up plausibly - I - you know - we're going to see him - the plot demands that he ages about a year a book, the plot demands that he comes of age in the final book. Now I have a real moral objection to books that freeze children in pre-pubescence even though they're actually - in earth-years - sixteen years old, but you're still - they're still behaving as - as eight- or nine-year-olds."
And you can find it here on this website: 1999: Accio Quote!, the largest archive of J.K. Rowling interviews on the web It's under part 19 (so a bit over halfway down).