While I'm not worried about these things, maybe I can help you feel better: DD doesn't wave or clap or babble with consonants.
The thing about these message boards is that people only bother to post if something is exceptional. You don't hear about the average stuff, so it makes it seem like your baby is behind when he really isn't.
When I do find myself starting to worry about stuff, I try to remind myself how babies start doing stuff seemingly overnight, with no warning. Up until a week and a half ago, DD wasn't sitting up on her own. Then all of a sudden, she started sitting up and pulling herself up on the furniture in the same week.
DD is teeny tiny too, but that's also not something I'm worried about. DH, while tall, was always a skinny kid, and I'm really short. I figure she just got both "small" genes! Don't worry about percentiles. Not every person can be in the 90th percentile. Someone has to be in the 9th percentile!
And developmental milestones are described in age ranges for reason. Now if your kid is turning 1 and can't clap, you might worry. But he still has time to learn.