There are several causes of bagginess of the eyelids
1. swelling – allergies are the number one cause
2. volume loss – when you lose volume in the central part of the cheek ( over the eye socket bone) it can give the impression that you have baggy eyelids
3.pigmentation – pigmentation overlying the bone can also give the impression that you have baggy eyelids. This can be caused by sun damage or simply thin skin with the underlying muscle showing through
4. fat – at your age it would be unusal to see excess fat as the cause but certainly a possibility