The most important thing is to respect them as adults. Introduce yourself, give some background information about why you are a clown and then begin your fun. Instead of twisting balloons for everyone- why not teach them how to twist and do a balloon excercise class
You will have more success if your program is interactive. You still may have to help twist for some due to limited mobility. Have a senior help with a magic trick.
Sometimes the biggest thing that can help you is to theme everything. Whether it be a holiday, an occupation, etc. That will help you pick routines, songs, and gags you can do.