Responses
he said he was to inherited from his parents, so its not complete impossible...
maybe the doctor went to visit and help his father at work, so that's when he saw Kotarou? ╮(￣▽￣)╭
Also, if you look at the little flash back of him as a kid, he only calls him yuuma. there is no mention of him being a doctor at the time.
Plus he could have just been in training for college
I can't understand the age difference.
If he was 5 yrs then the doctor would have been 15 yrs. So did he already become a doctor by then? #－.－)