5 years is the combined program! it's 6 years otherwise. child psychiatry is a 2yr fellowship. 38 is not old. If you want to child psychiatry you need to do the full training.
Many CAP fellowships are around 40 hours/week of work and have low to no call requirements whist allowing moonlighting (theoretically up to a total of 80 hours between all jobs per ACGME). This is how you would make extra income doing adult psychiatry call on the nights/weekends. Once you are a 5th year you sit for your boards and would be working as board eligible (aka attending) or even board certified once you pass.
I can understand the thought that most medical pediatric specialties involve no adult training but psychiatry is just not set up for this. The fellowships expect you to come in with all the knowledge of adult psychiatry which is relevant on a daily basis in child psych. They have a few peds portal programs that are 3 years peds, 3 years child psych but those are clearly setup to teach someone without any psych knowledge and are a year longer accordingly.
At the last AACAP conference, there was a town hall about starting a 3 year child psych program but you'll only be able to see children ofcourse. If it ever sees the light of day, it's at least a few years off.