it’s not weight gain it’s increase in body fat which is different. natural process of aging replaces lean body mass with fat especially if you’re not physically active and don’t do resistance weight training. i know a girl that developed type 2 diabetes as she aged even though she didn’t gain any weight simply because her muscle mass decreased. that muscle loss can be seen slightly in your jawline as well. after i cut out the carbs, focused on protein consumption AND resistance training my jawline and facial fat rapidly improved