That seems super ridiculous...you might have to keep the same basic theme and make a couple of different worksheets for low and high level, or a low level and high level activity. You could also mix the abilities for teams and get the older students to help the younger students.
Easy themes could be basic describing people. Younger kids you could teach big, tall, short, young old, etc. then get them to complete a basic worksheet while you carry on and teach the older students stuff like wrinkles, freckles, blonde hair, red hair etc.
Good luck.