What term retirement usually denotes to is, to stop working. People often don't like job, so to retire usually tends to be on top of the list. However, if one likes what he does, he will do something similar to pass the time even after retirement.
Now, I'll be honest, I dunno what I am driving at but I wanted to spark topic about retirement. Now, you go,
First, retirement does not entirely mean to stop working, it's just to stop actively working on a particular sector/job. This means that those who say they are retiring might have many activities they are engaging in that are fetching them money outside the main job, so it goes on like that. Especially if the person is making money through their hobbies or what they love doing the most, they, of course, would continue to do it while they retire from another job that might be out of passion or as a result of their age, time-limit by law and other considerations.
I can't even imagine myself retiring totally, this kills me more than anything. Human beings need active activity till death, this is so important if the person is such that doesn't exercise so often. Also, those people who I know who retired from their primary jobs in my country are still engaged in several activities, but the only difference is that they do it at their convenience time and with pleasure, not when they are forced to do it or have the influence of compulsion over them.
That's the difference, and again the reason why you hear some people saying they are "retiring to something." It merely means leaving their main job for something else, and this doesn't stop the person from earning as well, only that it will not be as stressful as before in most cases as they engage the latter with ease even as they consider their age.