Matthew is not sitting up yet. I have to say that my four year old has hyptotonia (low muscle tone) and didn't sit up until 9 mo, crawled at 13 mo and walked at 22 mo. I am so scared that he is going to have the same problems. She is doing well now, though, but it was a rough road. She also has febrile seizures.
You would think I wouldn't stress anymore with the third kid...
Re: Worried about my little guy
I think I'd go ahead and get it checked out if you're worried.
I don't know what the range of normal is, but DS2 at 7 months old was crawling and sitting on his own well and actually was pulling and standing before 8 months. DS1 was also sitting at 7 months, but not doing much else at that point.
I like how they've done this site. Maybe it will help you decide, but it sounds like you've got a couple reasons to at least bring it up with your Pediatrician.
https://www.earlyinterventionsupport.com/development/grossmotor/6-9months.aspx
wow - that's a great site! thanks for posting