This may help you some.
(Do a search on the Galvayne's Groove and that will show this groove)
Galvayne's groove. Galvayne's groove is located on the lateral surface of the upper third incisor. It appears first near the gum line at about 10 years of age. The groove extends halfway down the tooth at 15 years, and all the way down the tooth by 20 years. By approximately 25 years, Galvayne's groove is halfway gone, and by 30 years, it has disappeared completely.
The cups of the teeth are also used to help determine age.