I know that she was around 16 in the novel but I feel like they made her older in the movie. She certainly seems to act, look and sound older to me. I was thinking that she might be about 24, 25 at the most. What do you think?

I always pictured her as around 24. Because, she look around that age, and also because she marries Phoebus. He's the captian of the guard, so he'd have to be at LEAST late 20's (you'd have to be experienced, plus he says "You leave for a couple of decades and they change everything"). So I always pictured her around that age, plus she seems a couple of years older than Quasi.

I'm thinking 22 to 25

Well, concerning phoebus i think he more late 30's, because (if my memories are exacts) he said he leave Paris for a couple of decades, so i suppose he leave as he was a soldier to return as a captain.
Concerning Esmeralda, ipicture her as being 24-26 years old

I always thought she's between 26 and 28 years old.

she seems 30-35

I would say a range between 20-30. Quasi is 20, I would assume her age isn't that far off (though she's definitely older).

Probably in her early twenties. She definitely acts, looks, and sounds that way. :)

She is 15 in the novel, but in Disney's version, she seems older.

She is about 25, I suppose.

i think she's in her 20s

She's at least 20.