There seems to be no suggestion that there could be side effects just that the data is much more limited for over 65s. I don't understand Germanys decision.
The commentary at the foot of the link below is interesting. It says the reason scientists tested mainly the young was indeed to get the vaccines out as quickly as possible, though it doesn't say why older people were harder to come by, and that scientists were open about this at the time.
So presumably they are highly confident that efficacy will pass across age groups, even if all vaccines dwindle a bit the older you are.
www.bbc.co.uk/news/uk-55847387