Okay to start off with I hate the phrase "toy dogs", they are not toys and this is often forgotten.
I have chihuahuas and they usually live longer than most dogs simply because they are one of the few breeds if not the only one that isn't mixed with anything else. No one sat down and said let me put a dashound with a yorkie to make a chihuahua. This being the case, they have less genetic problems picked up from other breeds. All breeds have something. Hip problems, knee problems etc. Many chi's do have knee problems though.
Smaller chihuahuas do have more problems. The AKA won't allow a chihuahua over 6 pounds to show but actually the ones around 6 pounds or more are usually healthier.
Breeders who advertise "toy size, tiny, or tea cup" are to be avoided if possible. They merely breed for size and do not take into consideration how many problems the smaller ones have. Many "tea cups" do not live a full life. And the idea of a 3 or 4 lb female being breeded is an absolute horror to me.
Ricky is 7 lbs and although not "good enough" to show, I show him all the time to my family and friends. Lucy Tu is a little over 6 lbs and absolutely a doll. Desi Lu is 4 lbs but she is still growing at 7 months. I am hoping she will be at least 6 lbs.
Ricky's litter mate is 14 lbs and I doubt that his family would want to part with him because he isn't small enough.
Love your dog, not his size and remember it isn't the size that matters.

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