Melissa,
There is nothing for you to be concerned about here. He is right on track developmentally. He could take several months to master this one skill depending on so many varriables. He is doing so much more than learning to walk, he may be concentrating more on talking, or seeing, or any number of things that are also going on right now.
Don't under estimate his personality. He does not like the walker but would rather have company to help him along. If your little guy is one that takes the "community" approach to learning, then he has to wait for the comminity to be around enough for him to acheive mastery. Maybe he would rather not walk alone and has not figured out yet that he is his own independent person, and expects for you to be there when he tries to walk. Putting him in the walker says "do this by yourself."
He will get there. Unless you get past age two and have several issues that have you wondering, he is probably just fine. At this stage, you want to be on the look out for skills that he masters and looses, he is not to the point yet where he is behind.
M.