What you mean is someone not of an empowerment class (like a ranger) but seeking tattoo or some quest or favour. Whatever it is, you can start praying anytime you want during your life. However, for tattoo seeking, I will suggest at least 20 rank (some imms will require min. higher ranks) and above. Yes the praying process is about the same as an empowerment class, though with different emphasis, wording.

One needs to be well known in the lands to have a tattoo, or at least of some respectable status in the guild or cabal. Gods don't throw out tattoos just because you prayed often. it constitutes RP with others, PK-skills, the way how you deal with situations, tests, enemies, etc.

Hope I've helped you answer your queries.