Basically the issue with the knees is you don't want to start riding a horse too strenuously until the knees close. For each breed it is different. Some close at 3, others, like drafts and WBs, can wait until 5 or so.
the act of making or enacting laws. 2. a law or a body of laws enacted. Origin of legislation.
Legislation (or statutory law) is law which has been promulgated (or enacted) by a legislature or other governing body or the process of making it. Before an item of legislation becomes law it may be known as a bill, and may be broadly referred to as legislation, while it remains under consideration to distinguish it from other business.