The choice for who goes on a ventilator is very unlikely to be between a young fit person and an older person. The majority of those needing hospital care are older people . The average age of a Corvid-19 fatality is 81 with underlying medical problems.
The choice will be between two elderly people both with comorbidities. Me, say 77 and for this example, with asthma and high blood pressure, and you, possibly 5 years younger but with diabetes as well as asthma and high blood pressure.
The chances that any of us will go down in family history as giving up our lives during the Corvid-19 pandemic to save the life of a young mother, makes a good story, but is highly unlikely to happen.