I had braces as a teenager, because that was the norm then - ie wait until your facial bones stop growing, and then correct the misaligned or overcrowded teeth. I had them from the age of 14 until I was 17. No problems , 63 now, and they still look the same. (ok, maybe a bit more worn out!).
My Thai wife had a minor issue with protruding upper teeth and was quite self conscious about it. She had braces for 3 years to correct this, in her early 30s. The end result was very good, but she was still required to wear a 'retainer plate' at night after the braces were removed. She lost the plate and we had another made (5K!) - and after 5 days (the time to order and receive retainer)- her teeth had moved so much that it no longer fit! - as WBG mentioned above.
She now has a different retainer that she wears most nights, is comfortable for her, and her teeth still look great!