I've only had a quick skim of the replies, so sorry if my reply is a bit off track.

I just wanted to say that his gesturing isn't a bad thing.. and I personally wouldn't be discouraging it. If you read up on baby sign language and the benefits of it, you might find it a great way to help him start communicating. And it's shown to actually help them verbalise sooner. I found it really interesting how it aids the process.

I signed with both my kids.. they both signed back from about 12 months old.. and they both had a verbal word explosion around 19 or 20 months and it just went great guns from there. I wasn't concerned up to that point because we were already communicating.

Anyway, I just wanted to mention about the sign language. I don't know anything much about when delay becomes a concern, but it looks like you've received some great advice