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?
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.