Most are between 25 and 35. Some less-experienced people try out. Interviewees take two tests but don't have a formal tryout. I didn't, though I had requested it in my interview. Others got 2 days of SII training.
Formal training is minimal after the initial session that all new hires get.
I know I rambled on in an uncopy-editorlike fashion, but I disagreed with some of the information you had, and I hope this helps give a balanced view.