How to tell age of shama ???

Care to advise on the above ?

Some say shama leg's "skin" roughness can determine its age. But how about those whom soak or moist its texture with moisturiser or soap ,then peeling off its rough "skin" and vola !!! you got a younger bird.

So any other way to judge the age of the bird. Me really new in shama ,hope these question is not stupid.

By the way, how long can a shama bird live ???

Thank you