Not speaking after 2 years of age.

Hello doctor, My nephew is about 28 months old. He has been an active baby so far and has generally been healthy. However it's been a concern for us that he hasn't started talking yet. We've consulted many doctors but we've got a divided opinion. Some of them advised us to wait a little longer until he turns 3 while others say he needs occupational therapy immediately. One more disparity is that he generally responds to our calls and interacts fine. But when he's taken to the clinic for assessing his development doctors say that he doesn't make eye contact and gestures like hand clapping. Is that something serious to be attended right away or can it wait for sometime and he'll be alright in due course? Please guide. Thanks a lot