It's fine. He's young. My toddler and husband don't always respond haha. But seriously it's fine
My 9 month old is the same. And honestly my 2 year old too. I know they both hear but but sometimes they just don’t care to respond. But if I go closer to them kinda distracting from what they were doing they look at me.
I don’t think it’s a point of concern yet. If he responds when he’s not preoccupied he’s doing well. Also if you use nicknames a lot that could delay it