Depends. Some people are naturals, others, not so much.
it usually starts around puberty and gets better over time
Learning the rules is easy, but regarding how long it will take to master it ( and many players will tell you that you never will since the game continues to evolve) the length of time will vary from person to person and many will never be able to become profitable playing it.
Learning the rules and procedures is very easy.
Learning to play against other players always takes another 6 months, no matter how long you've been playing. Seriously. There are always new players coming into the game who will play with different styles. You'll have to constantly adapt.
Depends on several things which I won't list. For some people it takes a couple years, while others don't master it in their entire lifetime.
It depends what you mean by master. It's like asking Tiger Woods how long it took him to master golf. Even if you had practiced with him minute for minute, every day that he practiced, there is no proof that you would ever have been even half as good as him.
You could go hang out with any of the poker greats, and be given personal tuition from them for years, and still never have the specific skillset that allowed them to master the game.
Ultimately, it all comes down to what you consider mastery. Are you talking a one time win of a major tournament, or literally making it a full time income that allows you to survive just on your poker skills alone. Short answer is that if you have amazing talent, it may only take a few years. If you lack some of the fundamental skills, it may not be possible ever.
1.91 years if you have brown hair, 2.63 if you have blond hair
The best poker players in the world will tell you they never master poker. The game is always evolving so they need to continue developing their play. A better question would be, "How long does it take to become profitable?" Even at that, it varies by person. Some will get there in a few months, but only perhaps at on-line micro-stakes. As L. E. Gant said, some folks will never get there.
Some people never manage it!
About 2 years if you practice a lot like the hole day or halve but not practice adout 4-5 but I now you will practice and get better at it so 1 -2