To answer your question, I wouldn’t call it “indecent” to ask a woman’s age in the US, but it’s probably not advisable unless you already know the woman very well. :lol: (Even then you might have to be careful.)
If you ask a new acquaintance how old they are, you may well get a counter question such as “How old do you think I am?” And then, God forbid if you don’t underestimate enough! :lol:
I’ve decided that I’m also 26+. However, in my case, the “+” indicates quite a few years.