i have a brother with cp and i also have a daughter that was 2 months premature i think the biggest sign of cp would be in the walk or feet as he has to have special inserts in his shoes like braces so i would although you did not describe his age my brother was diagnosed within one year of his life. i would get it checked out but i don't think cp is a worry here.
hi, if the hand writing is well and he can do fifne movements properly it doesn't seem to be cp. but regarding the speech problem and prematurity it can be a kind of discordination in movement or clumsiness. you should pay more attention on activities which needs more speed and skill. such as receiving ball and trowing it in to a goal or basket, playing football and etc. can he use his both hands correctly? what about crossed movement?