High functioning autism. Until he s 3?

My son is 2 years 8 months.Im observing few symptoms like flapping hands when excited (only when excited).Sometimes when he is bored he will start running in circles with flapping hands with different facial expression. Also he gets excited if he sees water coming out of tap,blinking light.All these i feel he has high functioning autism.But his speech is fine.Although he wont talk properly.he is able to understand.And he can communicate sentences with 3 words.Also he was preterm born at 29 weeks.so all his milestones were delayed.so even speech is bit slow.but its improving.All other activities are good.he likes to play with kids.maintains eye contact.he knows alphabets,colours,numbers and he repeats whatever we say.he will respond to his name sometimes.but not always when he s busy doing his work.but he tells his name when asked. We are yet to send him to school.Only concern is spinning in circles with hand flapping. does he has high functioning autism or should we wait until he s 3 ?