My second daughter did not read until first grade. We didn't worry a ton, as her older sister also "read late" and didn't read until first grade. It turns out that second daughter is PG, and it also turned out that she is 2E (non-verbal learning disability). But once she started reading in first grade, she took off like a rocket -- she read the full Lord of the Rings trilogy in second grade. And had perfect SAT scores eventually on the SAT Critical Reading, Writing, and Subject Test in Literature. So at least for her, being slow to read was not a problem in the long run.
My advice is to keep reading to him a lot -- you want him to love books and language so he keeps reading once he gets the hang of it. In fact, I read aloud to second daughter until she was about 13, we just liked it as an activity. You may want to see about testing if he is still struggling by the end of first grade, though.
