I take pride in myself that I used only about 200 leves for all my classes to go from 50 to 60 within 15 days.

The key is really to keep burning about 6 leves per day on something, but not to go overboard too early (between level 50 to level 55). Then use more and more leves towards higher levels.

Always make use of EVERYTHING available, including GC turn-ins, Company-issued engineering manual (for manual crafting), Commercial Engineering Manual (for quicksyn post lvl 55), FC buff on crafting EXP, food to add 3% bonus EXP, go almost every item on crafting log, and then grind yourself on stackable ingots/lumbers.

When manual crafting, always try to push quality to max, it gives about 4x more EXP than quicksyn.

Once you have acquired enough stats, MACRO your craft so u can do it with 1 or 2 buttons. Then grind the hell on ingot/lumbers that you can macro on.

Towards level 57 to 59, massively do leves (and collectables if you run out of leves).

At the end, each class should only need about 25-ish to 30-ish leves to go from level 50 to level 60.

That's how someone get from all-50 to all-60 in less than 20 days (but this is assuming you don't gather all the raw mats yourself).

If you gather the mats yourself, it will take much longer - especially if the mats are random drops from monsters. In those cases, it's better to have more retainers. If you have 2 DoW/DoM retainers and 2 to 3 DoH retainers, they can do the work for you quite efficiently. If not, buying mats from MB is another option to speed things up.