I've had my Jack puppy for 2.5 months now (he's 4.5 months old) and I could not have imagined that he would be so good. I did my research and was prepared for the worst, so (despite living in the city) I arranged for a dog walker to come 2x per day while I'm at work + give him time to run in the morning and at night. I can't believe how easy he was to train. He sits, lies down, rolls over, gives his paw, and comes when I call him. I do spend much time with him and am very strict. My question is: should I expect him to get a lot more difficult as he gets older? What would be some good exercises to start challenging him mentally?