Scottish young people can and do go to Uni at 17. Some go from S5 - and even ds, who did S6, was 17 when he started.
So would similar kids be expected to start Uni, then go off to do their National Service, and then re-start their studies? Or spend one weekend a month "volunteering" - what about during their exams? Or the jobs that they need to top up their loans?
I think that @DuncinToffee has put her finger on it - Sunak is being trolled. I actually think that it is yet more proof that the Tories neither expect nor want to win the election.