Yes. The average age is 17-25...Older perhaps if you have been a "late bloomer". Regular dental visits can help prevent a lot of problems and most teens these days do have dental x-rays around 17 to see how those teeth are situated and if they will emerge properly. Many people simply do not have room in their mouths for these teeth.
Yes. Please keep regular check ups with your dentist to monitor your dental health.
Possibily. Normal eruption of 3rd molars (wisdom teeth) occurs between 18 and 22 years of age. Sometimes partial eruption of impacted wisdom teeth can occur after the age of 25. I have never seen full eruption of wisdom teeth after the age of 25.