We mature adults have all had our own life experiences which give us our own viewpoints. I accept that Martin, the 20 year old, didn’t respond to his situation as well as the poorly 15 year old, but I’m not going to compare them because, as you pointed out, brave Stephen Sutton was a young teenage boy who through his years of hospital visits had doctors and nursing staff who were experienced mentors in dealing with youngsters going through their high and low periods. I would also query whether he was left on his own for any length of time.
As for Martin, we know from the newspaper that he wasn’t on benefits, we also know he shared a flat which means he must have been finding himself some sort of short term casual work, but I imagine there’d not be much outside gardening with the rain we’ve had. We also know his mum had given him bus fares to go to the job centre. From the job centre, Martin went back to an empty flat with no job, no money and possibly no food in the flat. I know from my son and his peers how they were treated as 18 year old college leavers applying for benefits – all of them were chastened from the experience.
When I retired I did a bit of volunteering and came across some very despondent teenagers which prompted me to do some research.: ... The frontal cortex of our brains is that part of the brain where we sift information and then make informed choices. The frontal cortex is not developed in teenagers, they don’t have one at all until it eventually starts making connections. We know people develop at different ages, thus the only certainty we have is that by the time we’re 25 years old we don’t have a fully developed mechanism for evaluating and making properly thought out decisions. Until that time arrives emotions are the deciders to the choices teenagers make
I've now surfed and ound youtube videos which gives a better explanation - Here's a couple - one made by a male and the other made by a female:-