I could talk about "the path" for a long time but will try to keep it simple. Also, don't want to dissuade you or anyone else.
1) Many have discussed appearance, specifically shirts. I'd suggest one size down and really work on your upper body. You can tailor shirts if you have the money.
2) Many have discussed being "in shape". Huh? Have you seen all of the D1 officials on TV? You do not have to do much to look like them. Distance traveled for a game is around 2-3 miles, with much of it walking or barely jogging. If you can't do that, then you have issues far beyond officiating.
3) I found that getting advice from mentors and experienced officials was a bit contradictory to directives handed down from Adams/Collins/etc. Just before Adams, big-time officials were stuck "in their ways" and called a game they way they wanted, based on experience/level/score/etc. They were not as black-and-white (as far as rules). So, you might get great advice from some experienced mentor only to have someone like Collins tell you otherwise after the fact. Then it is too late, you have already made the mistake in some game. Find a mentor that is not too old/experienced or one that will advise based on NCAA leadership.
4) You may want to forget a lot about #3 because it isn't what you know but rather who you know. Find a D1 assigner and become their friend ASAP. To get into the Good 'Ol Boy network, you have to become a Good 'Ol Boy right? You asked why there were mostly older refs at the D1 level. That is because the money resides there. People tend to not want to give up money
5) Fork out lots of many and attend camps galore. That is where the path ends for everyone. After that, see number 4.
6) Work on spelling/grammar. ("latter" from your post)
