i think it’s very believable given his upbringing. also it’s not like he does nothing, but he doesn’t do any housework and stuff because well… he is a noble. when reading, i didn’t get the feeling that he acted like a kid, but i felt that he acted like a 20 year-old who grew up very sheltered.
growing up with strict parents (and immense pressure to be perfect) certainly made him meek with his mom, until they talked things out. and with mikado he was allowed the vulnerability that he was denied of during his childhood (because he needed to be perfect) so he lets himself get spoiled.
all in all i think aloy acts as expected from a talented noble who grew up sheltered but was also forced to suppress his emotions from a young age.
is it just me or does aloy feel rlly aged down- maturity wise. like i feel like his personality is a literal kid especially with his bf n mom. the pronoun switch to boku, not doing anythign, etc. idk maybe im being nitpicky