Everything really depends on your goals. Are you a completionist? Are you a competitive number-cruncher? Are you a casual player who stops to admire the view constantly?
I started from scratch a year ago and played for about five months until Aion came out. I had a friend who helped me out a lot with some missions, quests, and gear, but other than that, I largely PUG'd things I needed to get done and formed my own groups (or statics if necessary). By the end of my tenure, I had finished Zilart and CoP, and geared and merited two jobs to a competent degree. Anyone with the right mindset and support from friends can accomplish a lot in a very short period of time, thanks to some streamlining on Square-Enix's part.
You'll definitely be hard-pressed to run out of things to do.
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