For all the times I have been to the desert I have never seen small starts of a Joshua Tree before.
This was a first for me.
New seedlings may grow 3 inches a year for the first 10 years
and then slow down to 1.5 inches growth a year thereafter.
In the background you see one coming to its life's end. Joshua trees can take as long as 60 years to fully mature and may live 500 years or more.
The largest one known was 80 feet (24 meters) tall and thought to be 1000 years old.
Their trunks have thousands of small fibers and lack growth rings like normal trees do so it is difficult to tell there actual age in most case. The bark is extremely hard and tough. It'd have to be in that harsh desert environment which helps to conserve moisture.
I just had to show this picture again of my little buddy near a very healthy and handsome Joshua Tree.