Older and wiser?

I've just spent the last half hour reading over the months after Tank joined the family. We really didn't know what we were doing...I think we did okay in spite of that, in fact, Tank is a great dog right now. He turned 2 in February and he's just turned into this amazingly patient and very obedient dog.
Many of you know that we now have 2 dogs...and not just any old 2 dogs, no, 2 Jack Russell Terriers!
There are many differences between these two dogs outside of the obvious: Tank is a boy, Penny is a girl. We got Tank when he was 8 weeks old and completed his first puppy training class by the time he was 12 weeks whereas Penny came to us when she was 12 weeks and she still hasn't taken any classes because dogs have to have certain shots before they can attend said classes. Penny weighed 5 lbs at her 12 week vet check...Tank weighed 10 lbs!!
For a while here I thought that maybe Penny was a little slow because she really hasn't picked up on her name and while she's very energetic when she plays with Tank, she is also very unsure of herself around other dogs. I'm thinking that I might be very wrong about her...It's quite possible that Tank is slower than Penny. Tank has been with us for 2 years now and he's never found a way out of the backyard. Penny has been with us for 2 months and she's squeezed her way out of every little hole in the fence at least a half dozen times...I'm also quite sure that she'll figure out how to move the lock on her kennel and Tank doesn't even try to push on the door to his kennel to see if I locked it! The case is still out on this issue. Tank is amazing and not very typical for his breed and we're very happy about this, Penny may be more Jack Russell than we had planned for...but dang! She's cute!