breeder may have lied about puppies age...advice?

We want to get our pup spayed between 6 and 8 months old, as our vet told us that typically the earlier you spay or neuter (as long as it's not earlier than 5 months) the more of a docile "family" pet the dog will turn out to be. We were told our new pups birthday was June 22nd, which puts her at just over 3 months old, but she is a BIG dog. she's HUGE. so much so the vet said she looked more like a 5 or 6 month old puppy, and wondered if we'd been lied to. I started looking at imaged of other 3 month old pups on the net and it's true, she looks not just bigger, but OLDER than all of them. The fur is different, the body is different, the face and head is different and she's at least twice the size of any of the other dogs. I don't have any regrets, she's a beautiful animal and easy to train so far and very smart and gentle, but not knowing her age will affect stuff like the spaying (not being able to spay her at the age we choose to (which is 6 months) and will affect things like the fact we were told dominance challenges come strongest between 8 and 11 months. Even puppy potty training is supposed to be done differently for a 4 month plus old pup versus three months old and lower pups. The problem is that we got her from a farm that just happen to have dogs that reproduced and put the litter of puppies on ebay. They were an hour away from us and she was their last pup. They took the ad down and now we don't have a phone number for them. My husband thinks they may have lied because they thought that a 6 month old dog would be too hard to sell. But why would they lie? They live and hour away from us. Should we just get in the car and drive to their doorstep and essentially accuse the of lying to find out the true age, (and risk being wrong - maybe she just IS a big dog) and have it maybe be a wasted trip? Not knowing is eating me up, and I am sort of angry if it turns out they did lie. I'd have taken the dog anyways. We fell in love with her. but I want to be able to do this dog raising RIGHT and several months off could make a difference! (and explain a lot!) what should I do?

First off, what breed? Did you see the parents when you picked her up? She might not be purebred and whatever she is mixed with could be adding to her size.Second, to be a little less concerned with getting every little thing done at exactly the "right" age. I spayed my Lab at 6 months and I will tell you it did absolutely nothing to make her more docile. Shes still just as crazy as she ever has been. No matter what, remember you have a PUPPY on your hands here, who most likely won't be out of that puppy stage until shes about 2, maybe longer. Unless you actually have a male, or have another female dog in the house along with this pup, I wouldn't worry about dominance issues. Males are more prone to challenge you around sexual maturity simply because they're males and the testosterone (sp?) does that. The only time females usually display dominance is if there is another female in their territory. Like with my pup, she knows she's not "top of the food chain" at home, but if we go to a friends house who has a female Lab/Shepherd/Rottie mix they always establish who is the dominant one as soon as we walk in the door.Potty training should always be done the same for any age. The only difference is that the older the dog is, the longer they can hold their bladder. By the time I spayed my girl, she was potty trained. So spaying shouldn't really have an effect on that. If you're gonna go 6 months without potty training her.. Maybe you should rethink some things..Third, as far as confronting the sellers.. I wouldn't worry too much about it. Maybe they lied, maybe they didn't but as long as the pup is healthy and happy then I wouldn't bother. Plus, your vet should be able to accurately age a dog. If he can't.. Find a vet that can.