To be fair, the number of athletes killed by Covid-19 would probably be still lower than the casualties from any of the following: racist cops, Florida man, incompetent drivers, carjackers, subpar building codes, sinkholes, alligators, the weather...
You're just feeding into the misinformation about Covid-19, not to mention conflating fatalities versus casualties in your comparison, which renders it a meaningless bait-and-switch.
The FATALITIES due to Covid-19 in this age group is probably quite small, but the CASUALTIES is much higher than you're crediting. Even young athletes who were never hospitalized could be left with long-term disabilities. Just how many will suffer for months, if not years, if not the rest of their lives is an unknown because so far we haven't been gathering those statistics.
The overemphasis on fatality stats, as if that's the only downside to Covid-19, is missing the larger picture of this virus and the effect it will have on the health of the survivors.
And as for the Twitter post comparing Japan and Florida, all the MORE reason to cancel the Olympics. Because athletes from the U.S. will bring the virus with them when they come to Japan, as will all the other athletes from other countries. This is a guaranteed super-spreader event in the heart of Japan.