I've had two ends of the scale...one who started talking at 8months, could count to 10 at 1 and knew the alphabet and many many words in between at 18months and and then my DS who didn't say boo until 17months at least. There is no real time frame, unless you think he's not hearing properly or there's some other issue.

I talk to them both the same, and DS and I got along fine with a few signs he developed. He had the added advantage of a big sister who never ever shut up. All of a sudden only a few months ago (he's 25months) his vocab exploded, and he just knew words and what they were for.

Just keep talking to him. A daily narrative. Give him opportunities to respond - I learned this with DS (DD went to school and all of a sudden he had his chance lol). Read to him every day. Talk about the books. Sing......won't take long babe.