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?
Most foals will begin to lose interest on their own but if a foal continues to want to nurse, and the mare allows it, it is completely understandable for a foal to nurse up to 8 months old. (In the wild, mustang mares will often allow their foal to nurse up to 1 year old, or about 2 weeks before she gives birth to her next foal). In domesticated horses, where people have some control, it is best to not allow a foal to nurse over the age of 8 months due to concerns about the mares health and well being.