I thought the point of lockdown was to protect everyone, not individuals. So, although I am in my 20s and live alone, if I am out and about more, and catch coronavirus, I could be wandering around spreading it for two weeks without ever knowing- so putting all the people at the local shops at risk, and anyone I pass on my way to and from work as well. I live in a flat with shared stairs, so I'd put the other two flats in this building at risk too. It's not about protecting me, it's about protecting the community.
As it happens, I work in a school, so apart from my rota'd days, I obviously wouldn't be going to work in person until schools reopen.
I'm not really sure how allowing 20-30yos into work would really benefit anyone, and many work places would presumably still be closed anyway.
I think that study has rather missed the point of having a lockdown.