Kathlana,

If the character logged in for the first time less than 2 weeks ago, or/and is below level 20, the restriction is imposed. I.e., only one of them being true is enough.

As far as I know, this means that the level is relevant even after the two weeks. If a character has a level 1-19 job set as their main one at any point, fishing is rather fruitless. After the two weeks however, provided at least a level 20 job is being used, you should be able to get to the higher limit. ^^