No, age is not a factor. Our oldest patient is 64. So long as the gums and bone which support your teeth are healthy, you can get braces at any age to improve your smile.
Clear braces are made of white ceramic material which is more fragile and easier to crack. Therefore, they are usually used for top jaw. However, both types work on the same principles and tend to be equally as effective.
Orthodontics is not merely for improving the esthetics of your smile. Braces can correct malocclusions which can affect the way you chew, clean your teeth or feel about your smile.