I don't know how old is old enough to become an elder. But forty and fifty are old enough to be mature.

Honestly speaking, one doesn't even need to be an elder before exhibiting a sense of maturity. This is because one's life experiences and physical environment can play a big part in one's mind and way of doing things.

You can't compare a child who grew up in luxury with helps at his beck and call to one who grew up in a family that strives to feed maximum of two times per day, with the children in the family having to help out in their own little way. Obviously, his or her sense of responsibility heightens and this is a major element of maturity.

In the case of your cousin and the neighbour, I wouldn't say I'm surprised cause I've encountered such people and situations countless times. If one or both party doesn't get injured, the matter can never be settled.