Well, your not going to build those wonders obviously. I don't ever target a 'by turn xxx' due to the fact there are a lot a variables to deflect what needs to be a very direct path.
That said... how to get 4 workers fast is to
Build one
Buy one
Steal one
Social Policy.
That's a reliable you can do it every game sort of thing.
4 settlers I'm building 3 after a scout/monument/worker start.
By turn 45 will take a little luck, good tiles tight (not 3rd ring), probably a population from an ancient ruin plus a culture... even still it's rare to have the freedom to just do that, at least on immortal and deity.