Probably depends on how many dogs I have
I like to have an even gap in age.
Kobe is a bit over 8 years old, and will be nearly 9 when the puppy arrives. If I had two dogs, that would be about where I want it.
If I had 3, I'd want a 4 year gap. And so on.
The age gaps are nice, but it's also important to me that I don't feel like I have too many dogs to do the stuff I enjoy with (For example, hiking is exponentially harder the more dogs you have).
But at the same time I want enough dogs that I feel like I can always do stuff with at least one of them. So there's no strict rule, really, but I am going to try to keep them more spaced out in age in the future.