Women and 18-21 year olds got the right to vote after the 14th Amendment, and the way the Constitution gets amended (new articles that do not specifically update the provisions they modify) is prone to produce (at least, in the bare text; with litigation, some of this gets smoothed over in case law, though there's not a lot of litigation on the provision at issue to do that) incomplete updates and inconsistency.

  Women and 18-21 year olds got the right to vote after the 14th Amendment

To clarify: After, but not as a result of. (See Amendments 19 and 26)

Right, as a result of later amendments, hence why the penalty provisions of the 14th Amendment related to disenfranchisement don't take them into account.

(Sharp observers will note that race also wasn't explicitly a prohibited category until a later Amendment—the 15th—as the three civil war amendments, 13th-15th, were not ratified simultaneously despite being a related package, so blacks were considered in the disenfranchisement penalty clause before they had an individually-protected right to vote.)