Other things to think about are physical fitness and weather. Depending what part of the country you are in, acclimating to the weather at Great Lakes may be quite the change. As far as the Physical fitness, be working now on getting into shape. running approx 1-2 miles daily, approx 50-70 pushups and 40-60 situps. That's what i seem to remember the beginning pace as. Also, it's general orders of the
sentry, not "century". Try finding a copy of a "Bluejackets Manual", either at a used book store, Amazon, or library. Lots of good stuff in there.
Also, if you are not dead set on being a nuke, look at some of the other jobs, like MA, LS, CT, ST/FT.
Good luck and God Bless

You have the advantage of having the internet available to you, use it. Look at some jobs that seem interesting, and tell your recruiter you want to do that. Take a job that seems interesting, challenging, and that you think you would like, not just what the recruiter puts in front of you.
a few Links:
http://www.bluejackets-manual.com/