WEES. They are all so different. Its not just a boy/girl thing either.
Elijah was an early talker - recognisable words at about 10 months; 20-25 words by a year, 2-3 word sentences by 18m and full, complicated sentences by 2.
Sebastian is 15m and has no real words other than hiya, mama and dada. He makes a handful of other 'word-like sounds'; like 'u' for up, 'ba' for ball etc; but alot of them get lost in his general babble.
They all develop at different rates; and they also have different stregths and weaknesses. For example, Sebastian is alot more physically adept than Elijah - crawled earlier and much more competently, climbs everything and has excellent fine motor control.
I certainly wouldn't worry about speech until they were over 2, unless they struggle with comprehension, or are completely non-verbal. 
Noah Gabriel 11.06.05 
Elijah Cameron 28.04.06
Sebastian James 15.05.08
Nathaniel Joseph 04.06.10