Time goes by

[Miguel Madrid del Ama]

How much time passed between scenarios? Days? Weeks? Months? Years? Whatever you want?
If last question is “yes”, can you raise a character from 1st to 12th level in only one (in game) year? (you are a pretty busy man)

[Harley Quinn X]

The amount of time is undefined, so whatever you want, within reason. Some missions will take you out adventuring for several weeks during the mission alone. That doesn't even count the time it takes to get you to your next mission.

Logically, a level 1 character isn't in Cheliax for one mission, but then all the way over in Tian Xia the very next day, then roaming the Mwangi Expanse two days later without some serious magical intervention.

[Roac]

Generally it's assumed that one year of in-game time passes between seasons. But from what I gather that's not a hard and fast rule... so yes, you can level up in one year if that suits you.

[CRobledo]

My bard is level 10 and has only been a pathfinder for 8 months (yeah, we play a lot). I added one year to her age this weekend as well.

[nosig]

my wife runs a Aasimar Cleric (of Cayden) who is visibly pregnant. she created her with a dex of 8 and explained that the PCs low dex is a result of being at least 5 months pregnant. She often plays up the part of "being with child" (lots of RP here) and has reached 7th level now - still 5 or 6 months along.
Originally she had talked of adding her 4th and 8th level stat bumps to Dex, and said that it takes 8 levels to have a baby... but she couldn't resist adding the stat bumps to Wis.

[Michael Meunier]

Here's the problem with this though. Many folks don't necessarily play scenarios in season order and often jump around. So assuming each season is a year (and there's anecdotal evidence to suggest such) then my Bard must be a Time Lord or something. Ok, not really but the point is because there's no set order it's really hard to track things like age.

As to the OP's other question, if you only play scenarios than you can get to 10.1 in one season in theory provided that the tiers work out (I know, I just invited someone to do the math :P). Modules would be needed to actually push a character to "retirement age" in a single season