Yes, there is a risk of the infection having complications. However, the risks with COVID for that age group appear no different than for the flu - and yes, teenagers have died this year in the US from the flu.
I don't recall any "leaders" demanding teenagers restrict activity to mitigate getting the flu. It is accepted as a risk of living. But with COVID the reaction is horror that they might catch what appears to be for them a rather common cold.
Yes, young people can then spread COVID to others. But aren't we expecting and needing the bug to spread? It's not going away folks. Not anytime soon.
If one wanted to build an army of disease resistant warriors to go to battle against COVID, the best option is with young adults. Yet our "leaders" oppose this. Why?