The Bumbo and Jolly Jumper

Everly loves to sit in her Bumbo and watch us! She is often in it while we make dinner or eat dinner. It is really good for her to develop neck strength and control! She also loves her jolly jumper... Darren has been pestering me, basically since she was born, to put her in it! I was trying to follow "the rules" and wait until 3 months (that what "they" say is the age to start!)... One day, Darren just put Ev in it and she absolutely loved it! Who are "they" to say that you need to wait until 3 months???