You can encourage your adult students to complete each project for another person if size is a problem. The rules of sewing are the same whether you are 9 years old or 55. They need to be learned in the same order. One always starts with the simple skills and then adds more complex ones as ability improves. Give your older students the benefit of improving their skills at their own pace.
Time of completion is the main difference between young students and adult students.
The older you are, the faster you can work through each lesson. It is important for each pair of hands and eyes to complete each lesson. Sewing is one skill you can't learn by reading - you have to do it, and you have to do it over and over and over and over to get really good.