The blogger 'HD' has answered one part of your question and he is right. no need of sharing as it is a confirmed berth.
Regarding the other question of upper berths, = there is a provision just above the lower berth for to get to the upper berth. 50 yr old can easily get into that unless they have some physical problems. you can also request your co-passenger to exchange their seat with one of yours. i am sure somebody will do it. dont worry. have a nice comfortable and safe journey.