Hi M.!
I've read it can be absolutely normal for some boys to bed-wet until later in their life, even 9 year olds. That's why they made "cool" boxer-like sleeping underwear for them to wear at night.
They say that boys bladders sometimes don't grow until like 12-13, and the result is bedwetting. I remember when my 2nd son was 3-4, and we were on roadtrips, he couldn't hold his bladder AT ALL!! We had to stop all the time for his little bladder :o) My older kids were not like that at all.
I don't think your son should be made aware of your concerns, yet. He's at an age where he could be mortified.
I think you should talk with a doctor/urologist, to ask the simple questions first to decide if your son should even be seen.
In the meantime, try to limit any fluids after 6-6:30pm, to help the situation some. I do think your son is completely normal, though :o)
Good Luck!
~N. :o)