mimic cannaot duplicate there powers to the full extent, but x-man is the clone of cylops and jean, he's said to be the most powerfull telepath, rivaling that even of the pheonix but his body cannot withstand the full extent of his powers, when sinister created him he put a virus in him which effects his aging process and the more power he uses the more he ages, i heard though that he does not have the virus anymore, so im sure he can now finally explore his full potential