I started from scratch instead of butchering someone else's stuff, but since it's been 6 or 7 years since I've actually created an object, I had to dig up all the tutorials again. So far, so good, though. Sims walk around the tiles like they should, but it would be nice if pets and toddlers don't care and still cross over. They wouldn't care about a tiled path, right? I don't know if there's a specific pets/toddlers-flag, but I'm going to look into that. (Does anyone know?) I also still have to test with snow, make the tile placeable on a slope and locked tiles, make sure it can't get stolen and/or billed, and I'm sure there are other things I'm forgetting right now. Oh, and I have to make an invisible recolor.
But like I said, so far, so good.
To answer your question about age and pets, yes, there's a set of globals called "Age - Am I a [insert age]?" and also "Pet - Is Pet?" (and "Is Cat/Small Dog/Large Dog") for checking the Sim's age and/or species.
This is what happens if you don't make a simple table as your first object after a gazillion years.