Wow. Although that number in isolation is itself misleading as you need to know out of how many and it's easy to inflate it to 'out of all young people' where it's actually 'out of the percentage that tested positive'. An overwhelmed medical service will prioritise the young, so you'd get more young people in ICU in proportion to all people needing health care.
It shows the young aren't immune, but still doesn't tell us how age groups fair.
Also, there have been a number of mutations already.
https://www.biorxiv.org/content/10.1101/2020.03.15.991844v1
However, it's also possible that the disease is mutating into less-deadly forms as well if these reproduce faster. Evolution of the virus (selection pressure) will favour that which spreads fastest, not necessarily which is most lethal. It may be the virus that is most resistive wins out, but alternatively it could be the one that spreads twice as fast (exponentially) with minimal symptoms (so people don't isolate, causing more infection) is the one most people get (if such a thing exists) which may even help develop resistance against tougher strains - see cowpox versus smallpox.