Find the future age of each person. For example, assume that next year your team's starting lineup will be 34 years old, 24 years old, 30 years old, 26 years old and 28 years old.
Add together the ages of each person. In the example, 34 plus 24 plus 30 plus 26 plus 28 equals 142 years old.
Divide the sum of the ages by the number of people you have. In the example, 142 years old divided by five people equals an average future age of 28.4 years old.