Plutonium is much rarer in nature than uranium and is more commonly used for bombs rather than as reactor fuel. Like uranium, it comes in various isotope forms, with plutonium 239 the most commonly used. It is mixed with the much more unstable plutonium 240 to generate power.
It's my understanding that a horse's knees close around age 2- 2 1/2. My gelding JUST turned 3. A couple days ago in fact. Will a horse's knees almost certainly be closed by that age?
Thoroughbreds mature slightly earlier than quarter horses and other similar breeds. They are broken to ride starting around 18 months of age so that they are ready to race as 2 year olds. Warmbloods and draft horses mature later than average and may not be broke to ride or pull wagons until they are 3 to 4 years old.