I wouldn't be concerned at all. They all develop differently and at different stages. He'll get there when he's ready, and you're least expecting it x
My nearly 6 month old isn't putting his feet near his mouth, my now three year old never did this either and is bright as a button so I wouldn't worry! As for holding stuff, my 6m is only interested in taking his dummy out but not holding toys or anything else at this stage. I'm not worried xx
I agree with @Vicky , I wouldn't worry too much, also I try to pay attention to what they are doing as opposed to what the internet/others saynthey should be =D
My little guy is 6 months on the 11th of March, he can hold stuff but has only recently learned to do this (mastered it pretty quickly).... Absolutely no interest in his feet/rolling etc. I'm not worried because my daughter was exactly the same. She is now 2, developed totally normally (despite never crawling either) and is pretty advanced as far as speach is concerned. Babies are all really different and learn different skills at different times. Your baby has probably made other brain connections that other babies haven't yet. Try not to worry! I wish I hadn't worried so much with my first! Xx