Can retrognathism have negative after-effects? for example, your 20, then when your 40 years old, your jaw gets messed up with time, and needs fixing.

HYpognathia: Small mandible causes jammed teeth, which needs to be addressed sooner the better. Other issue, people with retrognathia is possibility of snoring and sleep apnea which needs to be address.

Yes: A retrognathic lower jaw places strain on the temporomandibular joint because the lower jaw must posture itself further forward than usual in function. This often leads to cartilage dislocation and degenerative joint disease. It also puts excessive occlusal forces on the back teeth resulting in root canals, fracture of back teeth and destruction of dental restorations. Headaches are also common.

Retrognathism: One thing to consider: when your jaws are misaligned, your teeth need to shift in order to come together appropriately. This is known as compensation. When your teeth are in a compensated position, they are not in an ideal position, and later in life this can lead to further negative consequences.