Is it possible to grow taller after 18?

Tough to stop: At 18 years old, your growth plates are still open, so some degree of growth will continue. The last of the growth plates usually close between 18-22 years of age. You probably won't grow much taller, but growth is still possible.

Sometimes: There are "late bloomers" or those who grow later than some. It all depends on whether your growth centers are still open. Your wrist/hand has many growth centers & an x-ray can be compared to standards. If your x-ray shows open growth plated you may grow taller. A study showing a bone maturity similar to most 14 yo would have several inches of potential while a study similar to most 18yo-not