I understand Harvey Milk didn’t get into politics or gay rights activism until age 40. Though I suppose being a member of the San Francisco Board of Supervisors isn’t exactly world class politician…
Elon Musk was around 30 when he learned enough rocket science to conceptualize and found SpaceX as referenced in this article. Depending on how you define “expert”, he could qualify since he runs one of the leading privatized space transport companies in the world now.
Cervantes had written poetry in his youth, but he didn’t start on prose (other than what was required for school work) until after his captivity in Argel. I’d be really worried if, having had access to schooling since childhood, he hadn’t put pen to paper (or rather, stylus to wax or coal to tablet) until age 13, but the skills required to write Latin translations, cuartetas and novelas are all quite different.
At that time, most writers were self-published (at least for first editions, if the work was succesful it might get picked up for reprinting), including him. So maybe he had been working on Galatea since his age was in single digits, but he hadn’t considered it publishable until he was 38.
TheRoman Emperor Claudius. He did practically nothing prior to his ascension to the imperium. He was a considered slow witted and harmless (he had some physical disabilities). Because of that he survived Caligula’s purges, but meant he had very little involvement in politics right up to his ascension on Caligula’s death when he was in his fifties.
Despite that he is considered one of the most effective emperors of Rome.
Well, eventually Prince Charles will also reach an OP “world class level.”
Green the mathematician, although he may disallowed in that he may have “started his discipline” young, if in an unorthodox manner, is interesting nonetheless in the OP general thrust, where extraordinary accomplishments in mathematics (and to a lesser extent music, chess) are almost always associated with “either-by-age 30 or none at all.”
Also ballet, it occurs to me…
I’m not sure this is what the OP was asking about, or that all of it is factually accurate: most of these are people who “started their discipline” much earlier, though they didn’t get their first big break till after 30. Rowling, for example, had been writing stories ever since she was a child and always dreamed of being a writer. It’s not like she was a novice at the craft at the age of 30.
Similarly, Jackie Collins first published a novel around 30, but she had attempted many works of fiction before then: she wasn’t “starting her discipline” with her first published novel.
Attenborough first applied for a job as a radio talk producer with the BBC at age 24, started working full-time for the BBC as a producer at age 26, during which time he first appeared as a presenter.
Stallone started writing scripts as a struggling young actor in his early 20’s.
And so on and so on. Most people who hit the big time in any field have had a lot of practice at it before they get to 30, even if they haven’t yet had any successes to speak of.
ETA: Oh, and Connolly was a folk singer who varied his songs with humorous introductions and comments, as folk singers do, long before he did an actual no-singing standup gig. Not exactly “starting his discipline” at a late age.
I just had to find a picture - https://www.youtube.com/watch?v=PJNoT392dm8
But had previously played baseball from childhood until age 24.