I think the thing is that even though we know that being young makes you much less likely to require critical care than you would be if you are old, being less than "critically ill" doesn't necessarily mean you won't get it bad. It just means you won't need medical intervention to ensure you don't die. That could mean that you still have respiratory issues and fatigue for months following infection.
There have been reports of "long-haulers" who've had debilitating symptoms that have lasted two months now.
We don't seem to have much in the way of numbers telling us how many people we can expect to be "long-haulers." The current data just tells us if it's "critical" or "mild," "mild" referring to a large range of severities. It could be a tiny minority. It could be sizeable.