Shemroon is a Trigonian, that means he's a cat-sized Dragon. every Trigonian has a specific element that they safeguard/control/are. Shemroon's element is Metal, all forms of it. he's capable of shifting one type of metal to another effortlessly, he can change the state of matter of metal from solid to liquid to gas without needing to alter their temperature. he can alter their temperature if needed but often doesn't need to. he's actually made of a large composite of different types of metal which means he can shape-shift himself in dozens of various ways. Shemroon is Extremely  old, but still maintains his extremely youthful attitude, personality, and youth. he often acts like a kid and should be represented as a teen almost. not too kid-like but not too old, he's one of the oldest characters in the series but that doesn't mean he seems like it. as far as personality goes he again is very kid-like, he plays and loves to have fun, he's extremely wise and often gives potent quotes, but he doesn't dwell on the past too much and prefers to look at the future and what it holds.
I imagine his voice to be somewhere in the 19-20 year old range, not fully adult but certainly not kid/teen. very uplifting and wise at the same time.