C.C.
I agree he is old enough to sleep through the night without any problems. Personally I had great luck with the BabyWise method - what finally made the difference for me was putting the baby to bed very early (around 6pm). Maybe you are already doing that, but if not, give it a try and that may make the difference. I found that my daughter slept very soundly and that her big sister didn't wake her up with the typical 2 year old bedtime routine.
Also what really helped me was the idea of giving the baby "big, full meals" rather than the snacks that my older one had been used to. In other words, I'd hold off on feeding her until she woke up from naptime/bedtime, so she would be HUNGRY when she woke up - and would eat a big meal. That big meal would hold her over 4 hours at least, at which point she'd eat another big, full meal. She would wake up after having slept 8+ hours at night, at which point she'd be ravenous. I'd feed her, and she'd go back to sleep for another 4-5 hours. So, I never had to use the CIO method because essentially she scheduled herself into sleeping through the night. It took a few weeks to get her sleeping through the night (she was a newborn when we started the BabyWise thing), but in my opinion it was totally worth it, AND painless, which was great. I'd recommend the BabyWise book whole heartedly - it's a quick read and made a HUGE difference for us.