How Late is Too Late to Redirect Pages of Domain for SEO

Imo it's never too late to upgrade seo. There are so many factors that affect seo (estimated 200ish) with Google. Definitely need to get your text optimized for rank brain and Google search (long tail conversational searches) I'm reworking one from the early 90s old Yahoo Builder. If you rebuilt it why do you need the redirects? Are you sitting on the old URL? What program is the new site built in?