two comments....
one, do not get a puppy. if anything, adopt an older dog. puppies and kids can be a nightmare. a dog's personality is much harder to judge when they are puppies.
two, my sister and i are 6 years apart. we are best friends and always have been. don't let the age difference play a factor. i am glad we are as far apart as we are. since i am older then she is, i got to teach her lots of stuff, and there was very little sibling rivalry. i think it worked out for the better.
you will know when the time is right. that is the way life works.
