From your statistic, I would conclude that it is not self-destructive for young people to be out and about. Whether it is selfish is another matter entirely. Taking an action that is beneficial to oneself, but harmful to others, is typically described as selfish.
Edit: To be fair, the same argument can be made in reverse as well, that it is selfish for older people to insist on universal lockdowns, which primarily benefit themselves. To that, I would argue (1) that death is not the only negative result from covid-19, and (2) that the relative magnitudes of benefits and harms need to be compared.
Edit: To be fair, the same argument can be made in reverse as well, that it is selfish for older people to insist on universal lockdowns, which primarily benefit themselves. To that, I would argue (1) that death is not the only negative result from covid-19, and (2) that the relative magnitudes of benefits and harms need to be compared.