The universe could be 27 billion years old if there is no dark matter. Then light would also behave differently than expected, and a few old theories would once again be valid.https://www.notebookcheck.net/Without-dark-matter-Tired-light-and-a-much-older-universe.814917.0.html
Well dark matter is a fudge factor, basically a mass number that was invented to make the calculations give the right number to validate mainstream theory. No evidence of it exists.