Amazon's rules state that you must be at least 13 years of age to sign up for an account. However, you must be 18 to make a purchase (since you'll need to input this data into your account before a purchase), unless you can obtain enough money in gift card funds to pay for the purchase or receive a gift card-debit card that has a major card company attached that you can input to pay for the entire purchase price.
The infomercial industry is huge and is worth a staggering $250 billion as of 2015. It all started back in the late 40’s and early 50’s when major sponsors of serial television programs were soap manufacturers (i.e. Proctor & Gamble, Lever Brothers and Colgate-Palmolive), which is how “soap operas” got their name. There is some controversy although the first infomercial is thought to have been for a blender either made by VitaMix or Waring Blenders and aired in 1949 or 1950. Time limits for commercials were imposed by the Federal Communications Commission (FCC) not too long after this which halted the growth of infomercials until 1984 when those limits were removed.