Can the eyeballs shrink or become more deep set as a teenager becomes an adult and if : how to prevent it?

As we age the retaining ligaments holding the eyeball socket fat inside the socket loosen. As a result as the fat moves forward and we develop pooching fat in the lower lids, the eyeball gloves sink deeper into the sockets creating deeper eyes and thicker creases if the upper lids. Correcting such aging is not easy and somewhat controversial. Tightening of the lower lids may return the herniated fat into the socket. Another way is to catefully add volume to the floor of the orbit to help move the eyes globes forward. This is fine in certain cases of orbit reconstruction. Peter Aldea MDMemphis, TN

One's face changes in a number of different ways from the teenage years into being an adult and also throughout adult life. It is highly unlikely the the eyeballs themselves have changed but much more likely that the structures around the eyes have changed. In some instances an eyelid lift or blepharoplasty can improve your look.