Hi ..firstly I don't think anyone can ever be sure exactly how big a Yokie will grow. We have a 7 month oldpup..the breeder told me he would be a "Teacup" as he was the tinyest of the litter..but he is 3 lbs. now with long legs....Also I don;t think that 4lb in weight is so tiny really.
I lost one in March..now he was tiny..weighing at 2 lb...he wasn't too delicate really...he was nearly 15 when I lost him..he was a picker eater and a bit on the nervy side..but all in all o.k.
I don't think you can really tell what they will turn out like really...but at 5 months old and 2.5 lbs. he will probably grow a bit more.. They usually say double the weight at 12 weeks..
Do you know anything about his parents..i.e. background as you say you are adopting him...Have you seen his parents etc.? Can you post any piccies of him at all.
I would say if you have taken to him then go for it...you should be able to jmudge the character of the dog at 5 months old...he should be sociable..not too timid..and responsive to you.
People who have had really tiny yorkies.i.e. under 1.5 lbs. may say they a bit harder to keep... but a 4 lb. yorkie should be just about right...and I think mine may be about that size as well.
Chrisann. x
