Last year my daughter was in first grade in public school, after being in a Montessori K and pre-K. Her teacher said the first "Unit" was all review, this was for math and reading. In my mind, the unit would have been a couple of weeks, but I think in reality it ended up being almost 2 months. She was bored and it was easy. I do think things improved a little after that.
That being said, it doesn't hurt to talk to his teacher and find out how the curriculum will change over the course of the year. Find out if what he has been doing has been all review (my daughter's was stuff she had done in pre-K). Some school districts do have G&T programs, in others, those don't start until at least 3rd grade. Before you push the teacher or the school, just try to get an understanding of what is ahead. Kids have very varied backgrounds prior to 1st grade, so I think they spend a lot of time on the basics in the beginning, trying to get them all to where they can progress.
Something you could do, if you think he would enjoy it, is go to a teacher supply store and buy a math workbook for 1st or 2nd grade level. He can do his own worksheets in that if he wants to challenge himself with math. They have "bridge books" designed to keep the kids brains from going to mush over the summer, or just a workbook for the year. He may find it fun for awhile to skip to the back and try to do harder stuff, or he may decide he has more fun - less work-like ways to spend his free time.