Under bite in the last 2 years my son who is now 24 has developed an under bite. I believe his bottom jaw is growing out past the the top. Do you know why this is happening and what he can do about it. Thank you.

Has he grown ? Usually by age 24, most young adults have stopped growing. There is about 5-8% of the male population that will have a post-adolescent growth spurt. This may cause a change in the bite. That may explain why he has developed an underbite now. I recommend a consultation with an orthodontist to determine the severity of the bite and help you decide on the best treatment for your son.
Answer: . Answer: in some rare cases the concluding amounts of body growth occur in the late teenage years and into the early twenties in age. If the individual has a growth direction pattern that promotes more forward lower jaw bone growth than upper jaw growth, the lower front teeth may appear as though they occlude (bite) on top of the upper front teeth. In some extreme situations the lower teeth will appear in front of the upper front teeth - some people call this an "underbite." to resolve this biting problem orthodontic braces treatment will most likely be required. In extreme cases the use of a surgical procedure to change and correct the upper and lower jaw bone relationships may also be required. The best way to determine what type of treatment is necessary would be to consult with a university trained orthodontic specialist.
Diferential growth. In a very small percentage (1.5-3%) of the population post-pubertal growth can cause one jaw to outgrow the other. In a miniscule percent of the population this is indicative of specific syndromes. Althoough your son's abberant groth has taken place at an age when most males have completed growing, it's not unheard of. Please see a dento-facial growth specialist, a fully qualified Orthodontst.