My son is 3 years and 2 months and we have just started potty training. He just wasn't ready before. So at 3 1/2, I know we won't be all the way there either. My first was a girl who also regressed after she started wearing panties, but she was 2 1/2 then, and was fully potty trained by 3. Everyone has told me that boys are later, and mine definitely is. I have found that he is more likely to pee in the potty when my 6-year-old daughter is with him in the bathroom. I know he's going because I can hear it from outside the bathroom. When I'm in there with him, he seems to get performance anxiety! So, I anticipate pooping to be a big issue, but we're not even close to that point yet. Good luck! As long as you're not putting him in a school that requires potty training by a certain age, you can take your time. It will eventually happen.