Joking with younger people and having a serious expression on your face when communicating with older people is wrong. The older subordinates would notice immediately that you behave differently to younger people. You would lose their respect and trust.
Do not force your authority too hard
Authority cannot be enforced. Rather, concentrate on collecting feedback that will help you find the right level of showing your authority. Solve any problems with older subordinates just like you would solve them with anyone else.
Fake it until you make it
It will naturally take a while for you to get used to managing older people. Until the time comes, pretend that you trust yourself and do not feel any uncertainty. Imagine how you would behave if it were really true. It will help you become really self-confident over time. Conscientiously hone your managerial skills and do whatever it takes to be a good manager.
-kk-
Article source QuickBase Blog - The Fast Track - management blog