I don't have access to that article but I think you would expect there to be lower risk for an elderly person if the younger people they have contact with have been vaccinated, but the issue is we cannot yet properly quantify the risk reduction. It may be minimal, or it may be substantial. My gut feeling is that it is likely to be closer to the minimal end of effect.

That said, I think older people shouldn't necessarily wait for their younger relatives to get the vaccine as long as they have had it themselves.* In some states/countries, it could be several months/over a year before everyone has access to a vaccine and I think people need to make their own decision on risk being mindful that isolation, in itself, is an established risk factor for poor ill health/mortality in the elderly.

*The caveat is, whether vaccinated or not vaccinated, everyone ought to continue to take precautions with respect to other non-pharmaceutical interventions in other aspects of their life (e.g. masks/distancing on public transport, in workplaces, supermarkets etc) until all vulnerable/elderly people have been offered the vaccination. At that point, given that we know the vaccines are pretty effective at preventing serious illness, we ought to start planning to reduce some of the physical distancing that is in place, although we will likely keep masks etc in public areas for some time.