A random observation that came to mind last week:
I've had many dogs throughout my life. But, there was only one who I got as a puppy. Muffin was about six weeks old when I got him. When I took him to the vet for his first check-up and shots, I tucked him into my shirt pocket and drove him there on my motorcycle... Honestly, he was that small. Every other dog I've called mine was at least two years old when I brought them home.
Cats, on the other hand, are different... I'm allergic to 'em. My allergies were very bad when I was young, and even today I still have pretty bad flare-ups. But, about 25 or so years ago I became brave enough, or stupid enough, or I just didn't care about my own health enough, and I brought this tiny kitten home. I fell in love with the little guy... Since then I've had about a half dozen cats (and enough boxes of Kleenex to keep the company solvent), but there was only one cat that I adopted as an adult. All of the others were kittens when I got 'em.
And, I don't remember where I was going with this...