Nonsense!
All you need for Ranked is basic understanding of the game alongside 2-3 Full Runepages and 3-4 Champions you don't completely suck with.
At Level 30 you usually had those capeabilitys (since they halved the required EXP for 30 I'm not entirely sure about this right now, but the original statement remains.)
I started Ranked the second I got my 16th Champion. Which took some time because I focused my early IPs on Runes and expensive Champions like Brand because I simply didn't know about the restrictions due to the Pick/Bann system.
So yeah - I started into ranked fast, have seen the Pick/Bann system the first time, had now idea about lane management or w/e and guess what.. I won games! Simply because I had a tiny bit of talent (like hitting Brand Ws!)
Because that's litterally all you'll ever need to win games in at 1200MMR!
I signed up for League mid Season 2 and ended up High Silver at the end of the Season... I wish anyone would have told me I get the gold cup with just 2-3 more wins... q.q x'D
So did it hurt me starting into ranked that fast??? I peaked at Dia 3 in Season 5 despite a lack of time due to study and RL in general! So obviously not!
So my iteration:
Congrats! You just hit 30, and you're ready to play ranked! Here's some helpful tips:
- JUST DO IT! It's not so special! Just 9 other guys playing the game just like you do! Don't be scared, but don't expect to much. Play and learn! Watch the more experienced Teammates and if you loose, don't get mad - just look at the game once more and try to figure out what went wrong! That's how you learn the most!