I took Angela until she was 11 to be able to open the dog kennels, and then only 3 of them. (the fourth requires significantly more hand strength than she can muster.) When we ask her to let the dogs out it is with a groan befitting most teenagers I know.
It took Axel about 6 months to figure out how to open the kennels, and he can open the difficult one too.
With the exception of the difficult one, it took Asher 12 days to figure out how to open the kennels.
We're in trouble.