Im definitely not making excuses for JLM and in fact have zero sympathy for him at all but I agree with the assessment about his maturity level.
The condition of Jesses car, the expired inspection sticker, his numerous garnishments, his living situation, the likelihood that he has very little money yet is a regular at local bars and his working what is basically an entry level job, his speeding away from police, getting into numerous fights....all of that, taken as a whole, is not what a person would typically expect from a 33 year old man.
Maybe a person in their late teens or early 20s. JMO
Sadly, I know a lot of young people AND not os young people that fit that profile. But fortunately none of them have been POIs in any such crimes. It seems to me that young adults are taking longer to grow up these days.
None of his issues are going to mitagate against any culpability, and they have not, as one can see from the long list of DMV violations he has had. He does not seem to be mentally handicapped as he does hold a full time job, has friends, has a car and a driver's license and seems to take care of himself, though not all that well when it comes to following the rules, My guess is that if one takes a random sampling of 32 year olds in that socio eco, they would have similar issues as JM. Hannah's disappearance is what put him over the top in terms of respect and being a respectable member of society.
The forensic reports, a lawyer who takes him firmly in hand, any other big development will have a huge impact on JM. If nothing shows up, or if what does pretty much clears him, hopefully this experience scares him straight on how he looks to the world and he works on become a more mature , responsible adult. I hope so, anyways.
If he indeed did harm to Hannah , then he is too dangerous to be loose in society and belongs behind bars.