Hi Crim,
It's never said explicitly their ages in the game, but it's implied that he's older than the others, since he was an older child (around 10+) when Miyetta was a baby and Mikaylis was a younger child (around 5+).
And yes, age doesn't necessarily equate maturity (or so I've found throughout my life experiences so far xD;;)
I'm glad you have so many thoughts about his character and I appreciate you sharing your interpretations!