I think that's totally normal and I would not bat an eyelash at it.
Does he turn his head when you say his name? Is he otherwise seemingly responsive to language? Because unless it seems like he's not responding at all (and could be deaf) then I wouldn't think anything of it. But if he's saying Mama and Papa then I suppose that rules out deafness.
ETA: A friend's son was not responding to his name and only babbling at well over 12 months....more like 18 or 20 months....and she was concerned he was autistic. Well, he's nearly 3 now and speaking in full sentences and in fact somewhat advanced in speech. He was just a late starter, but once he did he really took off.