I'm not an expert on this, but the last time I was using PNP crafting, the character needed to be a certain level to take each feat, but (in the case of +8 bonuses) the issue is not the character level but whether the character has the appropriate epic feat (craft wondrous item in this case). I think the initial feat only gets you up to +5regardless of how high the character's level is.
I'm sure you checked this, but also relevant is whether or not the chracter has enough gold and XP for the crafting.
Arbitrary crafting, which I use most of the time, isn't tied to character level either, but to feats gained, gold and XP available.