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this is my new fairy castle cactus also referred to as a green finger cactus(https://i.stack.imgur.com/ZpBSg.jpg)
It's virtually impossible to get an exact age. From the way these look they may be rooted cuttings which further obscures things.
Grown from seed, I would expect a plant like this to take 2-5 years depending on conditions.
Required, but never shown