Looking to Become a Shoutcaster

Where do I begin? I've had an interest in shoutcasting for some time, and decided to dedicate myself to learning how to become a shoutcaster. I understand it will not be easy and there will be a long time before I could ever be considered good at it. However, I would like to start doing it as a hobby and hopefully move into possibly shoutcasting professionally. I would like to shoutcast for League of Legends but I also have a big interest in CS:GO.

Now I suppose I'll provide a brief description of me. I'm 17, a senior in high school, and have been playing League of Legends for around the middle of season 3. I've always been fascinated with the game, even though I've only ever peaked at Platinum 1 so I know I'm not amazing at it. I have experience however with Diamond+ teams working as an analyst and I loved every minute of it. Researching LCS, LPL, LCK, LMS for pick/bans percentage, how often champions were played, champion winrate, different playstyles (rotations, laneswaps, objective control, counter jungling, etc.), researching opposing teams before any tournaments and working on graphs of the teams overall performance with what champions. I enjoy the research and knowing I am member of the team without actually loading into Summoner's Rift. A few months back there was an open tournament for ranked 5's teams and a buddy of mine was a moderator of the site that was hosting the tournament. He contacted me (knowing that I was an analyst for a current Diamond 1 team) and asked if I wanted to co-shoutcast the tournament to be broadcast on twitch. I absolutely fell in love with it. Since then I have been volunteering to shoutcast at whatever minor tournaments I was able to, but sadly I am usually turned down due to my lack of experience. I believe, however, that I am capable of shoutcasting games decently and want to start making shoutcasting my hobby.

I am looking for advice on how to get started, and where to go from there. Any and all help will be greatly appreciated!