How tall they are never bothered me, most people reach their final height in their teens, but I do agree that there are very few things separating the ages after teen, it's way too subtle. For me teenagers could be more lanky - like they have grown a bit too much in too short time - as many have that feature in real life, but mostly I'd love for some clothing and some hairstyles to be reserved for teens (maybe through a tag), so they don't go around looking like adults. Some hairstyles or clothes could make a teen look middle age (and some could make someone close to being an elder look like a teen).