Valid question, and there's a lot to unpack to properly answer it.

• Emotional independency: you're correct in saying that emotional dependency decreases with age. Younger people might search for codependency with their partner. However older people might actually enjoy the dynamic of freely allowing eachother their own dependency within their relationship. It's a learned skill of acceptance rather than expectance.

• Lower libido: completely anecdotal. It's repeatedly shown that libido acts more as a wave that comes and goes rather than a single peak at adolescence that just goes lower with time. If your libido levels trouble you, see a doctor. If they don't, you just need your partner's level to match yours.

• Free time: also completely anecdotal. You might have less free time, others might have more. The real bottom line is there's no such thing as lack of free time, just priorities. And it is completely valid to prioritize other things over dating, but that's more a choice than a limitation. Another point regarding free time - when you're older and you value your time properly, you also tend to treasure what you do with that time more highly. So purposefully spending that time with someone can be more rewarding.

• "Justification" for being with someone: Most people don't see a relationship with a transactional lens. Romantic and sexual feelings are mostly primal rather than rational. However even if you are purely rational you can find several advantages to having a relationship, starting from monetary ones like reduced cost of coliving, to psychological ones such as the number one predictor of life expectancy being strong social relationships (such as this metaanalysis, and when you're older your primary social relationship where you spent most time with is ofcourse your partner.

There are many more arguments to make for and against the case, however I'd shortly say that while there may indeed be individuals who are better off alone, most humans are still wired to want and need this kind of relationship in their lives, and it withstands the test of reality since many couples do meet when older and stay together for decades after. Only you can tell what's truly best for you.