I have a similar plan, my goal is to retire btwn 55-60 and do something I enjoy at that point.
I worked at a golf course in college, grounds crew. I really enjoyed it, it was a relaxing atmosphere (other than the occassional golfer who would hit into me while mowing the green or something). And I got free golf at the course I worked at and free golf at the other 2 sister courses (owned by same company).
There were a few retired ppl I worked with and they would work 3 days a week cutting the fairway, rough, etc. Several of the starters and rangers were also retired and worked there a few days a week.
From a pay standpoint, it was a little better than minimum wage. I was on the general crew (not the greenskeeper or assistant keeper), so I cut greens, fairways, fixed sprinkler heads, general landscaping, etc. Nothing too difficult.
To echo what WUTiger said, it will really depend on the need for staff when you start looking to actually do it. But it shouldn't be too tough to get the job if the timing is right.