I think my worry stems from the fact that I have a lot of friends with kids his age. They are all stay at home moms, and spend a lot of time teaching their kids...and of course they have a supportive spouse as well. Some of these kids are already reading when they start Kindergarten. There's a 1st grader in my circle of friensd that is reading at a 6th grade level. Everyone keeps telling me that Kindergarten these days is not what it used to be, that is it more like 1st or 2nd grade...that kids should be reading, counting to 100, etc. My son is a very social kid, funny :) argumentative :( and sometimes makes statements that makes me stop and think :) but he I think I'm worried that he'll be behind as he comes from a broken home, and while his Dad loves him and is very involved in his life, is not as involved in "teaching"...so he doesn't get the constant attention my friends kids get when it comes to academics.
My mom is a first grade teacher. She, and every other quality teacher I know, says that reading is developmental. The early readers are not necessarily the best readers by 3rd/4th grade. Some kids learn to read at 4. Others are closer to 7. Learning first doesn't mean you'll be the best/smartest, just like learning to walk early doesn't mean you'll be a great athlete. My friends daughter went from not reading to reading Harry Potter in 6 months, but she didn't start until early 1st grade. Honestly, parents love to brag about their kids' early prowess, but it doesn't indicate intelligence, and your son won't be behind just because theirs are "ahead." My DD is in kinder now. Some of the kids are reading, some are still learning their letter sounds. All of them are right where they are supposed to be.
I guess it depends where you live, but I live in one of the highest achieving, best districts in MA, which is one of if not the best state in the nation for education. It is absolutely NOT required that kids ENTER kindergarten knowing how to read or count to 100. My DD didn't. I am super glad our district hasn't bought into the whole "kindergarten is the new 1st grade" thing. I think it's much more important that your son is social, happy, and imaginative, and that he's exposed to plenty of time for creative free play. Drilling academics at age 4, while it does produce excellent party tricks, does not produce critical thinkers and problem solvers who will ultimately be successful in life.
You, and his dad if he's involved and caring, are doing a great job!