Mushloom,
I wouldn't worry too much about Ivan either. Ethan isn't talking yet, not a single word, and we're fine because he's just not ready to speak yet. But he does understand what we say and he takes instruction well, so I think that in part shows that he's developing fine so to speak.
I'm sure Ivan is the same?
Anyway they're all storing up all sorts of knowledge now and when the flood gates open, then we'll be wishing for them to shut up
Besides, it is true that boys are generally slower in comparison.
My friend's son only spoke his first word after age 2, our boys still have a few months to go so just wait and see.
I reckon that if he isn't speaking much more by 2 or after, you can seek some professional advice if you like.
But don't worry, Ivan's saying a few words already!
Ethan looked at me and said 'mum' once, got me all teary eyed emotional and never said it again. Go figure! Haha