Sounds like your child may very well be ahead. My personal suggestion is homeschooling. It's the only way to keep a gifted child from getting bored (or frustrated if you try skipping him a grade)...
However, with being a single mom this could be more difficult. If it's your mom or a relative or a one-on-one person who watches him, you could see if they'd be interested in doing it with him. However, those are usually more expensive (unless they're a relative)...
You can check with the school about getting him a placement test and maybe starting him in first grade instead of kindergarten... But, then he's going to be with a bunch of kids who are older than he is...
There are also gifted programs at a lot of schools that help keep smart kids challenged. You can look into seeing if your school has one...
Otherwise, it'll be up to you to keep him challenged. Give him skill-appropriate books when he comes home (or make sure his after-school babysitter gives them to him). Come up with fun math games to keep him challenged, etc.