I don't think its changing much, I recall back when I was a kid and just started to find furry things online. I think that would be about the same time as the OP. On my end the over all ratio of adult to non adult oriented art is about the same, or if anything I think it may have shifted more to the non-adult side. When furry things started to circulate on the internet at first, you know back in the baud modem days, the people online to talk about and do furry art were older. There were not as many pre/teens online so the artwork, stories, and comics tended to reflect that.
Now in today's modern culture where seemingly everyone has internet as a child, the average age I think is declining. With that comes issues two fold.
*1 : people are more... randy from ages like 15-25 and then it naturally declines. These are also in my experience the age ranges of most furs I meet IRL. I meet very few grey muzzles and very few young ones. So it stands to reason that anything that can be remotely sexualized, will be by this age group. See anime, videogames, commercials, clothing, books etc all aimed at this age group.
*2 : But the fandom still has a great deal of art that is safe for work, lots of it is even what I would call fine or high arts, the Blotch Duo comes to mind with their amazing inking and watercolours. it all depends on what you are looking for and where about you are seeking it.
I have artwork from back in the mid 90's that's pretty hard core, and some that's softer and more suitable for all ages. Just the same as now when you go to an artistic sharing site like deviant art, you can find artwork aimed at all the age groups.