Do you think things through at all? Let's play your scenario out.
Let the "young healthy" people out. Quarantine old people. Young healthy people get sick, 50% don't show symptoms. 40% get sick, 5% die or need hospitalization.
You're going to count on that 50% who show know symptoms to never come into contact with elderly/at-risk people? That 50% will continue to go out and spread it to more younger healthy people and the cycle continues.
Old people need to go out and buy essentials and run errands too. The 5% who need hospitalization will put a strain on hospitals as they become sick around the same time.
The only effective way of managing this is mass quarantining as the disease is too new and the hospitals are clearly overwhelmed. Give up temporary freedom for the sake of everyone else and stop being so shortsighted. People like you can't see past the one night of fun you may miss out on. Frustrating as f