It is not easy to pinpoint a gecko's exact age unless you have had him from birth. The pet store or breeder you purchase from should be able to give you the creature's age when you purchase a pet; otherwise, you can use weight and length plus color and markings to approximate an age.
Weight and Length
Leopard geckos are the largest gecko species; they grow to between 8 and 11 inches. Babies at birth measure 3 to 4 inches and weigh 2 to 5 grams. It takes about a year for a gecko to reach adulthood, at which time a female measures 7 to 8 inches and a male 8 to 11 inches. The female should weigh 50 to 70 grams and the male 60 to 80 grams. You can tell the difference between a mature male and a mature female by checking their undersides. There is a V-shaped vent by the tail base: Males have visible pores here, while the females' pores are difficult to detect.
Color and body markings provide some age clues. For example, the gecko may become more yellow as he ages. Also, baby geckos have band markings. Around 1 year old, the bands turn into spots.
Based in London, Eleanor McKenzie has been writing lifestyle-related books and articles since 1998. Her articles have appeared in the "Palm Beach Times" and she is the author of numerous books published by Hamlyn U.K., including "Healing Reiki" and "Pilates System." She holds a Master of Arts in informational studies from London University.