in america for premies we use what is called an adjusted age it works by subtracting the amount you were early from your actual age ...its kinda weird then as the children grow they start spliting the differance in half by the time they are thre they dont adjust except for micro preemies which then carries until age five which by then they presume should be fully caught up .....my son is actually going to be two on the 12th of july but when you adjust his age ...he was 4 months early his actual time of turning two would be his due date of nov 6 ...so in july we would adjust him by half and he would then be considered ten months old on his second birth day ,,,lol its alot to figure out and keep track of lol