OCD and ADHD symptoms definitely overlap. For example, I have the habit of checking things several times. Like, I'll check 10-15 times to make sure I didn't leave the oven on after I've finished using it. However, I do this checking because I know that I have a poor attention span, and I know that even when I double or triple check things, sometimes I still screw up. So, I check things multiple times just to make sure I didn't screw up. Hopefully that makes sense.

As for having ADHD symptoms pre 12: Well, sometimes it's hard to recall our childhood. I never suspected that I had issues before 12 years old, but when I came across my old report cards from school (1st grade through 5th grade), I saw a lot of comments about me fidgeting and squirming in my seat, being talkative, getting distracted, etc.. It helped reaffirm my suspected ADHD diagnosis.

After that, I did a full psychological examination to determine that I indeed had ADHD. (My insurance covered it 100%, so I didn't mind doing it.)

So the most important thing you can do is try to understand the reasoning behind your OCD tendencies. e.g., Do you check things a certain number of times because you feel you "need" to, or do you check things multiple times because you're coping with your poor attention span? Things like that.

Hope that helps