I'm sorry you are worried
First off, I want to say that I personally believe you are doing all the right things. Staying positive and making life a fun learning experience for him. Repetition and modeling are extremely important at this age! Keep up the great work.
At any young age, what is considered developmentally appropriate will vary. Like Melanie mentioned, I would consider the list of developmental milestones and consider what he is/ is not yet doing. Julie also mentioned a great point, that you may see some differences since his is the younger of two.
I find it difficult to measure the range of developmentally appropriate skills of a 2 1/2 year old from personal experience as J was always ahead of the curve. I'm currently noticing differences between my two boys and find it hard to not get that feeling of concern for T, but then I have to stop and I realize that I cannot compare the two! I can't use J as my baseline, but that is all I know from personal experience. When I look at the textbooks, I find that T is within the range of normal development....
As far as seeking help at this age, I would initially start with the pediatrician and then go from there. A learning disabiltiy would not be as obvious at this young of an age (and his brain is still developing!). What is most important is the stimulation and learning experiences that you are currently providing to him. That is going to help him tremendously! You're doing a great job!
Mommy to 2 amazing little boys!
Angel babies 6/9/07 & 11/16/07