25 miles is a lot for a kid who is not used to biking. Just because he is a 16 year old kid might make one think he must be in shape. But it may not be true. Also, even if the kid is active, biking is a skill and certain techniques like shifting, climbing, and especially drafting come with experience. If you want to take less experienced riders with you, then you need to adjust the pace and just enjoy the scenery that you can see better now that you're going slower!