We got Luke when Paco was 8 months old. We wanted to make sure that Paco was 100% potty trained and reasonably disciplined and accustomed to our household. It worked out fine in terms of the age issue. We were told that it did not much matter whether we got a second boy or a boy and girl, as we planned to neuter/spay them anyway.
The big surprise for us was the huge difference in the innate personalities of the two. Paco is outgoing, gregarious, unbelievably smart and fears almost nothing. He is a bundle of energy and curiousity, and remains so at almost 2 years old. He loves to play with us and his toys. He can be very competitive when he plays..he's got to always be first to the object when playing fetch. He loves to cuddle when we are in the same room together, but is not a velcro dog. He can be stubborn when he wants to be. When he was young, he would often growl at us if we tried to interfere with what he wanted to do. It took some training to get him to be the well-behaved dog he is today. He loves to look out the windows all day long, and knows how to interpret everything that goes on. He is very flexible about his space...not territorial with us or Luke.
Luke is cautious, very gentle and loving with humans, can be fearful, doesn't understand toys and has been a much slower learner. He is velcro with a capital V. And yet, he is not much of a cuddler...just wants to be near you, not on you. He is very eager to please, and constantly looks into your eyes for your approval. He is not curious, hardly ever looks out the window, and clearly enjoys his long daytime naps more than Paco does. He still does not get the point of a game of fetch, and is not competitive at all. However, he is very territorial and possessive of us. If he's sleeping next to us and gets the feeling that Paco is horning in, he'll actually growl at him. But he's never growled at us...he becomes putty around humans.
Needless to say, the first two months together were difficult for them. Not because of the age issue, but because of the huge personality differences. Paco wanted to play with Luke, and because he was 1/3 Paco's weight, and not much of a playful pup, Luke would run and hide. We had to keep a constant eye on them. When Paco rough-housed, Luke would growl and snap to make him go away. But Paco is so playful, he didn't catch on for many weeks that Luke was not like him.
Anyway, the adjustment period is now well over a year ago, and the two of them have become inseparable. We can't even take one on a walk without the other. If one needs to go to the vet, the other one goes along for moral support. They learned over a period of a couple of months to have more respect for each others needs and wants. Paco learned that Luke does not have an insatiable appetite for play, and will leave Luke alone when Luke has grown tired of play. However, Luke learned that a little play can be fun, and often will be the instigator when he is in the mood for a game of chase. Paco learned that a little growl means "go away." He also learned that a little cry means he is playing too rough. Over time, Paco moderated his behavior accordingly. Now, if they are play wrestling, and Luke lets out a little cry, Paco's tail goes down and he immediately starts licking Luke as if to show he didn't mean it.
I think they are very happy to have each other...But...
I think if it was up to Luke, he would have preferred having a companion who is quiet like him. A dog who could hang out with him for company, but not necessarily interact all that much with him.
Paco, on the other hand, loves having a dog companion for fun and adventure. If it was up to him, he would have preferrred another dog just like him, so they could run, chase each other, play tug-of-war, and just generally romp all day long.
I wrote this long story because I would never have believed that two dogs of the same breed who each came to us at 10 weeks old could be so different. I really worried during those first two months that we made a terrible mistake. While we are now absolutely thrilled to have them both, and truly enjoy them for their differences, it took quite a bit of work and close attention at the start.
I recommend that you think in detail about Scooby's personality, and what type of personality the second dog should have to best complement him. A good breeder will be familiar with the pups in a litter and, if you describe Scooby, will be able to help you pick the right one.
We actually had two terrific breeders. Luke's breeder did listen to us carefully about Paco, and she accurately described Luke. However, at the time, we thought another dog like Paco would make the two of them too wild and competitive. A quieter, gentler and eager to please pup seemed like the right choice. It took a lot of patience to discipline Paco when he was very young, and we didn't want to go through it again, or have a second dog reignite Paco's less positive behaviour. But Luke turned out to be even quieter and more withdrawn than we expected (or maybe he was just overwhelmed by Paco). We should have realized just how unalike they were when Luke's breeder told us that, if the other pups in his litter were playing too actively, Luke would go away and burrow under a blanket. He no longer does that, but it was his escape from Paco for many months.
In any case, while they started out more like polar opposites than variations along a spectrum, it has all worked out very very well in the long run. I think that most dogs are trainable and most pairs of dogs can be taught to make a good team. The difference is that some require little human effort to accomplish the task, while for others it becomes a labor intensive project.
I hope this helped.
Harvey, Paco and Luke