Answer:
Yes! There are a number of reasons for having an adult Bar Mitzvah - you may not have celebrated it when you were a child, you may have converted in later years, or you may have experienced a spiritual awakening, and you want to mark your commitment to the Jewish people again - as a mature adult.
You can have a bar/bat mitzvah at any age, although there is a custom to have a second bar mitzvah at age 73.