It is my experience that just because you can spend xp in an area does not mean it will be allowed by your GM. Games that continue for years need a certain amount of artificial limiting in order to provide the best play experience. Rather than jacking up your piloting or gunnery you will end up diversifying your skill base. This keeps the game a challenge (and thus fun) without the GM having to resort to pitting the PC's up against enemies who shouldn't rightly exist.
While I'm certain it is more than possible for a PC to start with 5's or 6's in their main area of expertise, I know the life path system doesn't leave a whole lot of points for everything a player may want. Consider starting lower toward the 3-4 value (3 is green, 4 is average). Most characters start young (less than 25), and thus there is no reason you need the value of a veteran or an elite soldier. Leave yourself some room to grow over time (that doesn't mean as soon as you can afford it), your GM will thank you.