Here's my conspiracy:
They are aging them up because they intentionally want to see the furry community get in on it. They saw what the characters did when they first aired (and were underage mind you), they saw what Lola did, hell they saw what Animaniacs is doing with the Warners who most don't find attractive, and most of all they saw what Zootopia despite objectively not having sexualized designs. And that leads to a massive fandom who actively contributes new material, tens of thousands of porn images, and other stuff which Disney is only slightly capitalizing on. And they want to capitalize on that.
They know what gets people on, and they know Babs and Fifi already do so. They aren't going to overly sexualize them, but confirm they are at least 18 (if not more) so porn artists are more eager to make art of them. They are going to make Babs and Buster fully a dating couple so that pairing is encouraged. Fifi is going to be in the show just for this reason. And they hope more people view HBO Max and maybe buy shit if they make another big furry fandom product