Well here is what goes on at my house
Doodlebug was neutered at 5 months and was 12 weeks when I brought him home. Within a few weeks of coming home he was lifting that little leg of his and marking everything! He is still a little marking machine and is now almost 2 yrs old. There isn't a bush, fire hydrant, tree......get the idea.........that is safe from this little guy.
Bogey was well over a year when he came to me from a shelter. He was not neutered but NEVER lifted a leg to mark. Within a few weeks of being adopted both Dbugs and Bogey were neutered together. He still squats when he pottys.
Pebbles (female) will not only mark but she lifts her leg too
She was spayed at 5 months old. She didn't start the leg lifting until she saw Dbugs doing it when he was a baby.
Now the funny thing about my boys is that Dbugs is my marker but Bogey is my humper!
He doesn't hump any of the other dogs or even stuffed animals but he will hump the AIR. You don't even realize what he is doing until he really start to get moving. When I tell him to stop he usually does but I have to say it is pretty funny. This didn't even start until about 6 months after he was neutered so I really don't understand this little guy at all.
I guess my point is that you just cannot predict who will mark and who will not. Girls, boys, spayed neutered it is all a mystery to me.