you have two factors in your question that are open to interpretation: the age of a ‘healthy senior’ and the size of your class.
I saw in your profile that you are certified as a personal trainer but are not a group exercise instructor; thus I assume that you really are doing personal training.
As you are NASM certified, you would do a certain degree of assessment and then tailor the program to the results. Exercises for ‘seniors’ do not necessarily need to be any different from that of other age groups given the same level of ability.The only things which I observed to be consistently different are the ability to generate power and exercises that require quickness and agility because it has often been many years since more mature participants have done that. (Which is not so assume that every younger adult is good at it.)
I hope this helps.