The twenty years between Anakin’s fall and ANH is really set in stone.
That’s actually an interesting point, because if you use carbon freeze/relativistic time dilation on Padme, you can really fix a lot of the issues with the timeline. If in Episode 3 Anakin was in his thirties along with Owen and Beru and Obi-wan was in his forties, you could simply have the twins be conceived then put Padme on a ship at sublight relativistic speed for a while. When she returns ten years have passed for the galaxy but for her it’s been less than a year, whereupon the twins are born. The Clone Wars could take up to ten years longer, the Jedi would be practically extinct for an extra decade, Anakin would have given up hope of Padme’s return…and Anakin would believably be in his sixties by ROTJ.