After you finish your character's first lvl 10 guild quest.
Though if you're looking to sell stuff on the Market Boards, you'll have to quest until you unlock Retainers, which comes with completing your first Copperbells Mine run.
Otherwise, I suppose you could exclusively do leves, though, without retainers, I would imagine your inventory is going to fill up fast.
Vrrynn Moonshadow (Mi'qote / Ul'dah / Faerie )
SCH 50 (/*-*)/ WAR 50 (and the rest are works in progress)
Vrrelle Moondancer (Mi'qote / Limsa / Faerie)
PLD 50 (rawr~) MRD 29
Vrrllyrr (Mithra / San d'Oria / Seraph)
Drg 75 (I <3 Lumi!)
"The problem with black and white, is that is turns grey at all the points of contact."
"I feel its an insult to Mithra everywhere that rabbits can /check as 'Tough' instead of 'Lunch'"