that depends a lot with the growth conditions. if they have been kept in a thriving climate (much light in the shadow, 30-35ºc and water every time the soil is dry in the summer and left alone in the winter, watering only when STRICKLY needed), the should be around 1cm in diameter. if they are tough boys and learned to survive in another climate, then they can be pretty small. i know a baby peyote that is TWO years old and is not more than 5mm in diameter, and about 1cm tall. and he has a brother that is still smaller than him, but they both live, so they must be pretty adaptable and strong. how have you treated it ?
i really enjoy cacti, not just peyote. i have a little collection of them, maybe one day i take some photos and post them here. cacti are like an addiction to me. i cannot visit greenhouses or large malls with some cacti. i always bring one or two, and i am running out of space to store them in good conditions. and after that, there's a fantastic thing that you can do: mix polen from one cactus to another and see how their son will look like.
edit: you can calculate with some approximation what the age of the peyote when he is young that he grows about 1cm each year. then this stabilizes and he begins to get fat and look like the first picture. i would say that that peyote is about 20 years, maybe more. the number of that little tufts of hair is also important. the more older, more hair. i would say that the peyote grows 1cm in diameter until he is 5cm (5 years). but your results may vary.
i have read many times the myth that the peyote is the slowest growing cactus on the planet. this is not true. some species as the ferocactus, pachycereus, pilosocereus, and many others are much slower, not to mention the flowering time from seed.
peace!
