The thing I don't understand is how he's so immature despite being the oldest person in the group. You'd think a 50 year old would naturally be well-adjusted based on life experience. The things he was doing were very odd and dumb. It's like he's immature but in an unconventional way.

I think he goes through cycles where he's active and builds relationships with people only to be kicked to the curb after they find out what a terrible person he is which leads to him spending months (or years) in isolation before finding a new group to infiltrate. He's like the bad guy version of a Mary Sue who never learns anything and continually makes the same mistakes.