My baby doesn't mimic sounds

I'm going to bring this up at our nine month appointment in 2 weeks but does anyone else have a baby that doesn't mimic sounds? He definitely can hear okay. He responds to his name and follows commands like "clap clap" and when we ask "Where's Harvey?" he will grab a blanket and pull it over his face to play peekaboo. He also babbles appropriately, with mamamamama and dada dada being included in the mix. He also mimics motions (waving, patting on the back, etc.). He seems intelligent so I am not incredibly worried but I think he's supposed to have been mimicking sounds for months now. Did anyone else have a baby like this? I feel like maybe he's just being defiant, lol. He also doesn't really do a back and forth with us when we talk to him.