In my opinion, he just might not be quite ready to wait 4 hours. With my DD, I tried to "guide" her to 4 hours around 4 months, but she wasn't having any of it. Then, a few weeks later, she started napping longer and naturally stretched herself out to a 4 hour routine. I think the 4 hour/4 month recommendation is more of a guideline than anything else and if it doesn't work, it can wait. If his naps and everything else are going well, I wouldn't worry about it just yet. Of course, this is just my take on it and I'm sure you'll get other ones