What kind of condition is social skills developmental delay?

Later Than Expected: Studies have shown that most kids follow a pattern of advancing skills regarding use of various interactional skills..There is a tremendous range of time, so a child may smile at someone as early as 1-2 mos.And as late as 5-6 mosand still be in the "normal" range. When these advancements are delayed, longer than the expected latest normal time, we worry about problems.