Hey Zionite,
I can only confirm that you can obtain Titan at level 35 so far (as i am only level 37 myself). However, in order to accept your level 35 Summoner job quest (in order to obtain Titan) you must advance a bit further in the main story line quests. Eventually (I believe it's a 33 or 34 main story quest) you will be required to use the duty finder to kill titan. Once you have done that, you can accept your 35 summoner job quest. This quest requires that you solo Titan then complete a second fight. After you turn in that quest back in Gridania, you will obtain Titan (please note that your summon II spell will still look like carbuncle).

If i find out more soon I will do my best to update this thread.

Hikari Nosenshi - Cactuar