Cas, either option is fine -- it's up to you. In our case, we brought our son for three reasons. First, we cruise for the experience of being at sea, even way back then. Second, I needed a vacation as I had a stressful job outside the home. Taking care of your own baby isn't a big deal. True, it may limit some of the activities you had grown accustomed to -- you just find new ones to take their place. Another reason is that both sets of grandparents lived nowhere near us, and couldn't take more than a few days away.
But, I would still wait until the baby was a year old (or so), and definitely get clearance from his doctor.
The other thing is that we didn't have to fly for this particular cruise. Flying with a baby is far more difficult.