Ranma, Akane, and I think Kodachi are 16
Nabiki, Tatewaki are 17
Kasumi is 19
Gosunkugi is a freshman so he should be 15 or so...

Gosunkugi is in the same class as Akane and Ranma.  He is 16.
Akane and Ranma are also Freshman

Mousse and Shampoo's ages are not listed, I  would guess 16 or 17.
Genma, Soun, and Nadoka are in they're late 30's or early 40's.
Hinako Ninomiya is like 21..
Happ and Cologne are about a couple 100 year old
Ryu Kumon is 16 or 17 I think...
Ukyo is 16 I think...

Yep. ^_^ Ukyou is 16

Ryouga is 16 I think...

Yup ^_^ Ryouga is 16

Tofu is in his 20's
Shinnouske is about 16 or 17
Tsubasa is about 16 or so...

Tsubasa is 12 or 13

Akari is either 16 or 17...

Akari is 16. ^_^

Kunoichi- ummm I'm not sure...
Herb, Mint and Lime- I don't know
Gambling King, Picolett Chardin, Saffran, Shampoo's dad, Jusenkyo's Guide,
that big cat, Principal Kuno, and Sasuke.  beats me..

*********
* Mihoshi@Ara?  Furinkan High?  Wai, Mihoshi didn't mean to crash here...