Throwing more variables at a question we already have an answer to is a waste of time.
We know that older people get it more, die more, and are more at risk under all circumstances.
Also, with vaccine production ramping up, a lot of countries project that they'll have vaccinated everyone by summer. Who cares if there's a better model? Elderly + frontline healthcare workers is a good enough model, go go go!
You are wrong about the first part. There are way more under 65 infected than over. And I've seen some preliminary studies that they do 80%+ of the viral spreading.