I see the poodle I think but it could possibly be schnauzer or a wirehaired terrier. I think I see jack russel but could be rat terrier, or who knows. I dont see chihuahua in him though. he is adorable by the way.
judging by the first pic where he is next to the pc mouse, I would say he is around 8 weeks old. but in the third pic with your hand on him he looks a bit bigger, maybe 12 or more weeks old. hard to judge age, if you had a purebred (just for instance) german shepherd it would be easier to estimate age. with a mixed breed of questionable breeding it is difficult to say.
cute cute cute though.
oh...I would expect typical terrier behavior. IF he is poodle x terrier he will probably be a bit energetic, really smart, very playfull, and very easy to train with positive reinforcement. many jack russels (many terriers for that matter) are extremely tenacious and resourcefull. be prepared for a dog that will elarn how to open the latch of a gate, climb over a fence by getting in the corner and climbing jackie chan style. they like to dig. they have great prey drive = love to chase small animals like squirrels. also very very good companions.