We are on AFF
I’ve tried absolute lines only to find my writing crossing them. Minor1 was the first to fall, when I had an otherwise good premise, and the MC’s sister (13 year old) found her way into the story in a more major role than I had originally anticipated. I considered changing her age, but then the MCs would have to change their age, and that’d affect other stories as I’m tying a bunch of them together (it’s more of world building than simply story telling). So, in the end, I just require good reason to go with younger sexual activity. (Though I do have younger nudists.)
Like BW mentioned, I let the characters be themselves, they can explore what they want to explore … its not like they listen to me In extreme cases, I can always have their parents/others walk in on them ….