Hi J.,
I am no expert but my son and daughter couldn't be any more different.
My daughter met every milestone like "as I was reading the new milestone" hahaha
My son, it is all at his pace, he held his bottle at NINE months ;) my daughter did at 5!
Things like that... waving, eating...
I guess each child has their own personality AND pace ;)
If the peditrician hasn't been concerned, I would just give him a little longer.
Oh the worst one so far, he wasn't sitting up until he was past 8 months!! - They're supposed to at 6!
He was crawling and turning all over, but not sitting up....
I was worried and now he's sitting up at 9 months perfectly ;)
Amy