YES! Thank you! The brothers DO have ages! The number of years may very significantly from that of a human lifespan, but I have it on good authority that Sess (in the feudal era) is 19-ish, which and that makes Inuyasha 15-16-ish. The manga puts Kagome at 15.
Yup. :3 In appearance, Sess is 19ish, and Inu is 16ish...though their actual ages are suggested to be much greater than that. Based on the third movie, which isnt completely cannon but many of us consider it to be, it says the inu no taisho is killed about 200 years prior, which would make inu 200 years old. At that point in time, Sess appeared to be 16-17, so we know he is /at least/ 200 years old at that point..but since he is full demon, his aging is probably different from inuyashas, and could be older.