Iddah is the waiting period before a husband can have sex with a wife who is not a virgin in order to guarantee paternity.
"and for
those who have not menstruated the period is three month.
And for those who are pregnant, their term is until they give birth."
I'm sure you are aware that women don't menstruate when they're pregnant, and the verse that you quoted previously refers to that.
And if you had read your Quran you would know that those who have not yet started menstruation is a different group to those who are pregnant, as highlighted above.
Just in case you still aren't convinced, here are the tasfir of some classical and modern scholars...
"(along with those who have it not)
because of young age" - Ibn Abbas
"those who have not yet menstruated,
because of their young age" - al Jalalayn
"
The same for the young, who have not reached the years of menstruation" - Ibn Kathir
"They may not have menstruated as yet either
because of young age" - All Maududi
Of course, you can argue that they are all wrong and you are right, but in matters of understanding the Quran I defer to the tafsir of renowned Muslim scholars rather than some random apologist on the Internet who doesn't even seem to have read the Quran properly. With all due respect.