SB613: Your point does have some logic but it isn’t persuasive since halacha itself says, both, to get married younger as well as to wait for an older sibling. Waiting for an older sibling isn’t a newfangled svara; it is brought down in the seforim hakedoshim. Halacha doesn’t say to get married older for societal reasons. (In fact, as we acknowledged, halacha says to get married younger.)
(As an aside, it is also interesting to observe that it is usually the same people who will push for getting married older that will also push for not waiting for an older sibling.)