I wouldn't worry at all. As long as he can follow your directions, he hears you, and babbles/has a few words, hes FINE. You cannot compare children at all, even within the same family.
My oldest didnt' speak at all until he was 2 1/2, and then he literally woke up one day and started speaking full sentences. I'm not joking, he went from 5 or so words and grunting/pointing to speaking clearly. BUT he was very physical, at 5 months he could sit up, at 7 motnsh he was crawling and cruising furniture ,adn walking at 9months. He picked up a screwdriver at 14 months old and started turning a screw, he was physical, but not a talker.
Now my youngest, he was a talker, by 9 months he had 20 words, and by a year was making sentences. Now at 2 1/2 he speaks fully, we can full conversations with him and total strangers understand him. But he's a big ol klutz, he didn't walk until 11 months, he atually never walked, he went straight from cruising to running! LOL!
ALL kids are different, and I don't think its a boy thing vs. a girl thing (that really bugs me, I know its because I have two boys, but I get REALLY tired of hearing 'oh boys are slower, they learn slower, they develop slower.. blah blah 'because I don't think tis true. I think all kids develop at thier own rate, I've seen girls who babble at 2yrs old, and boys who talk clearly at a year old. Each kid is different, and that stereotype really ticks me off.
If you wnat to have him evaluated, go for it, but honestly I think its an overkill, he sounds like he knows what he wants, he understands you, he just needs to 'get there' verbally, and he will.