Seems like you're reaaaally splitting hairs here. Young age is okay to discriminate against, but not old age (because you don't leave old age without dying). Anything people can enter and leave by choice is not okay to discriminate against if it's -important-, like family or religion.

What about menstruation? That's pretty universal to women (not entirely especially with non-cisgendered), not really a choice (at least, not without encroaching on the same protections you'd want with pregnancy), and all those who do menstruate enter and leave it (both monthly, and at menopause)...what's your objection to discriminating against menstruating women?