I think the point is, while lots of people argue that getting a job at 18 may or not be easy, OPs son doesn't seem to have even tried.
She says he's at a cross road figuring out what he might want to do. While claiming UC and spending it on the food he wants to eat as he's 'fussy'.
So need to think he's trudging round rainy streets applying for hundreds of jobs through tears like he's a Victorian street urchin.
Same as no need to think OP is struggling with a severely disabled child.
The benefits system we have had for a while now has enabled lots of people to decide it's a better deal than working, or just easier. Or preferable. For many reasons. Some lazy, some just for convenience.
And then people fly into a panic when some of that money is removed because e.g their child has reached a certain age.
And then some MNetters get all up in their feelings and engage in outrage about how there are so many reasons why work couldn't be an option for those people and imagine that benefits were always at a subsistence level akin to almost being in the workhouse in the 19th century.
When actually, it has been for years, a very good alternative to working for people that qualify.
OP was receiving £300 a month just to cover for the last few years, a teenager. And has 3 other kids she claims for. And doesn't work. So has been housed and her lifestyle comfortably financially supported for the state for however many years and now that's been reduced, people are scrabbling round to excuse why both she and her adult son might not or outright can't, work and how unjust the system is.
The gravy train has just slowed down, not completely stopped. Though some posters think OP and her son and presumably her other 3 DC who will be adults some day are being victimised in people ever expecting them to get a job.
Because there will always be a reason not to in these kind of families and the cheerleaders on MN will always come up with a way to support that.