Never thought about it with RM2, which I’m only a novice with anyway, but I’ve tried ‘0-level’ characters two ways in MeRP:
The first is pretty straightforward and logical. Since 1st level characters are assumed to have 10,000(?) xp under their belts, just give them an amount less than that, give them no profession (and thus no profession development points), and there you go. The downside is that there’s little room for variation between characters outside of hobby ranks, at least until they level into a profession.
The second method was to start everyone off with the civilian profession, call that ‘level 0’, and then let them pick an adventuring profession once they level up. This does essentially give them a free level, but it’s pretty much all in background skills that rarely see play, so I didn’t notice a difference. You do have to fiddle here and there with how to interpret level bonuses.