It is perfectly OK. Indeed, the fact that he holds a pencil at all shows that he is doing fine.
Try not to compare your DS to other children. It will only make you sad, smug, or deranged!
However, if you need reassurance, remember that there will be kids going into his class who have just turned 3.
Your DS must be one of the oldest, and I speak from the position of having a child who is one of the youngest in the year, at the beginning of school your DS will have a massive advantage over the younger kids. It's not fair, but thems the breaks.
Another thing to do is to realise that you child is not just about ability. Obviously he is the most precious thing in the world to you, and you want everyone to know that he is so ace, and it can therefore be a bit heartbreaking that he does not seem to be as 'good' at doing things that other kids are. This is a bit of a red herring.
I look at some of the kids who are advanced in my son's group of friends. And some of them are, frankly, not very nice. I would much rather have my sweet natured and kind little boy, who is averagely able, but who is happy, and who brings a huge amount of joy to our family.
When I see some of his poetry spouting contemporaries pinching their siblings and telling their mothers that they hate them, I'm glad that I have my little duffer, who adores his siblings, and is basically lovely.
But back to your issue. if it upsets you, just stop seeing those friends. I had one friend when my DS was very little, who was a really nice person, but her son was very advanced next to mine. My DS has not even saying car, and she once brought him round to show off his newest word, it was 'hovercraft'. I backed off after that, because rather than enjoying the time we spent together and the support we had given each other earlier in our children's lives, her insistence of showing (and I don't think it was showing off) her son's abilities in the face of my child's lack of development made me sad.
I know I should have risen above it, but frankly I was not mature enough to do so.
Good luck. You'll be fine. And so will he.