He's probably tired now that he is older and probably napping less during the day. He's probably ready for an earlier bedtime, like you said. Also, many kids have a "witching hour" of crankiness. My girls were always crabby before dinner, and my little one always gets really crabby in the hour before bedtime.
I would establish a nice bedtime routine that you do every day so that your son knows what to expect and knows that he is expected to sleep. With our 7-month-old daughter, we do bath, lotion, story, feeding, and bed. We put her to bed with her pacifier (a big soother for her) and turn on a white noise machine. It has worked well for us. Good luck!