I'd say this is the worst time to start getting into LoL.
I used to love this game. Started playing during the beta and to date have played roughly 2400 games (usually 30-45 minutes each!).
Used to be, this was the casual MOBA while all the hardcore people played DOTA or Heroes of Newerth. People would scream at you about EVERYTHING in the hardcore games while LoL just let you pick what you wanted, go where you wanted, and it was cool.
Sometime around the time the game went "pro" and started championship seasons, that all changed. Streaming and Twitch TV of the season finals suddenly turned everyone into a pro and the rise of the dreaded "meta" was upon us. The meta meant that everyone decrees there is a "correct" way to play the game. Currently the meta is sustained brawler top lane, jungler, AP burst damage mid lane, support + dps carry bottom lane.
Absolutely no other way will be tolerated. You will be shouted down, swore at, and rage quit on for deviating from this in the slightest right from the hero selection screen. The days of trying out double mid lane, no jungle, or dual lane, or Ashe in mid, or whatever you wanted to do for FUN are long gone.
The thing that gets me, is that I could understand this from serious top level competition, because right now it is the most optimal setup, but the advantage is slight enough that only about the top 10% of players can really capitalize on it. But in unranked bronze level games? Who are these people kidding? There are five hundred different more important things you could be doing at that level than worrying about lane composition. You see clueless amateur stuff like people geting ambushed ("ganked") by the enemy jungler three times in the first 10 minutes and never buying a wad, but those people will still lecture and cuss you out over lane composition.
If LoL was a Basketball game, lane composition would be what type of sneaker you're wearing; the edge it provides is slight and only perceptible at the professional level between players of equivalent shooting and passing ability. Freaking out over that in Bronze or unranked games is like being scolded for not wearing $300 sneakers to a local pickup game by a guy who can't even dribble.
At this point, League of Legends is as hardcore anal as Heroes of Newerth was. DotA 2 is now the official "casual" version despite having a more complicated laning phase, hero skills, line of site rules, and item shop. At least you can mostly pick whoever you want and go wherever you want without much harassment.