The age of the model wouldn't really be a consideration for me
Provided that the groups were not posting nudes purely for prurient interest, I would have no issues with it, provided that said groups had clearly delineated folders that separated mature content from other non-mature content.
When I was doing photography I only shot with models who were of age. Mostly because of the hassle of obtaining consent and the inherent complications arising from requiring parents to be present at any given shoot.
Now I just draw and don't need to worry about such things.