YABU
My DD is in similar position, heading for 20, didn’t want to continue studying at 18 and has no idea of a long term career move. So she carried on with her retail job,, with plans to go abroad travelling/volunteering.
She spent 10 weeks on the other side of the world last autumn, doing some volunteering, all paid for by her earnings. She was lucky to get an unpaid sabbatical and is now back working, saving to go abroad again in late summer, this time hopefully to do some working as well as travelling. She plans to resign and is already realising that she wants something better (with no idea of what, or if she has she won’t discuss!)
We know others like her in similar positions, the girl who she hopes to travel with got A/A* at A level (my DD did a BTEC) and then worked in a bar, she is currently volunteering in a third world country.
A friends DD is similar, brilliant A levels but no idea of a career so is doing retail work and travel.
They are still so young, and it is pointless them going to uni just for the sake of it.
DS is finishing a degree, and has a definite career in mind - DD sometimes says “Why don’t I know exactly what I want to do like him” - I reply because everyone is different.
I occasionally have thoughts like yours, ie when will she decide what she wants to do, but I quickly squash them. She works hard, helps at home, cooks, saves and, despite lacking confidence, travelled across the world to volunteer with people she had never met before. She might not have the career sorted, but she has guts and a work ethic!
I also occasionally want to kick her out, but that is usually due to teenage strops more than anything else!
Give your son time, and be proud of what he does. Like others say, him and my DD could be far worse. Maybe suggest he uses some money to go abroad in some capacity?