SPEECH DELAY?

Hi. My son is already 21 months old this coming May 4 and he is being compared to other kids who can say several clear words and some who can sing the alphabet. Me as a mother is hurt when hearing comments like that because I believe that maybe my child isn't ready yet to talk and I do some readings regarding speech delays and acc. to what I've read, parents should be worried if a child is already 3yrs old and still not uttering or speaking. I am just a bit worried I know. I don't want to be affected by those people commenting non sense things or anything about my son but I admit that sometimes, I really think of it seriously. My son could actually utter some words, clear words such as DADE, WOW, NO. I am also teaching him ABC but his attention span is too short so what I do is I just let him point out to the things/pictures then I'll tell him what is that. He can recognize some pictures though. He also do eye contact when we're talking to him. He also grabs our hand whenever he wants something and we consistently talk to him and even let him play with other kids or be surrounded by other people who can speak with him as well. I don't know mommies but I am being paranoid already. I fear that there could be a problem with my son's development but at the back of my mind, it says that it is still too early to tell.