I'm not sure punishing veteran players and punishing those that strive to get higher gens is necessarily the answer here.
The real question is how can we help genuinely new players get to a point where they're not immediately turned off from the mod? Starting them at Level 15 is a good suggestion. I may also suggest that within the first 30 days of registering their c-RPG account, they are allowed to freely-respec their build(s) and possibly have a 30 day boost to xp?
Not sure how that could be abused, but I'm sure it could be. This is why I shouldn't weigh in and make suggestions or state my opinion at 1:10 AM.