We use both 才 and 歳 to mean age, and I think they are interchangeable with each other. There might be some difference between them, but I don't know and I think almost all Japaneses don't care about the difference if any.

i think japanese just use the 才 as a short term for 歳. because the 歳 is difficult to write... but the original meaning of 才 is ability，talent. eg:she is talented.=她很有才. as num said. and both chinese and japanese share the meaning.

O(∩_∩)O~I am not sure about what you really want to know,but in Chinese,they are totally diffrent.歳 means age，it is a measure word. 例She is 10 years old=她 10歳了 才 means ability，talent. for instance，she is talented.=她很有才. It is also can be used as adv，which means just ，only. Let me cite an example，她才十歳=She is only ten years old.

look at this sentences：I found them in other place and translated them in English，coz I am not a Japanese major+_+，anyway，hoping can help you. 歳いくつ？2才/歳です。 How old are you ？I am two. In Japanese，they share the same meaning，which means age. 歳（とし）いくつ？歳 act as subject，no need to add number or なん in front of it，here the 歳 pronounces “とし” 2才/歳です。here both of them can pronounce“さい”