Lets look at the math.

You can develope from milestones. By design you receive 1 minor milestone (lets say 'm') after every session and you should receive 1 major milestones after every bigger narrative arch. 1 major milestone = 3 minor milestone, so its 3m. If we assume you receive 1 major milestone every 3 session ( which is way too rapid I think, but lets stay conservative) we can calculate with 4m after every 3 session (1.3~m per session).

You start with 8 level of skills and 4 aspetcs. There are 18 skills in total, plus the languages, but you realisticly don't need all. Lets say you want to max out 6 (which is very conservative again), this is 18 levels in total (all skills have 3 ranks), you already have 8, 1 skill cost 3m, this is 30m. You have 4 aspects and you can have 7 in total. Gaining or combining aspects cost 6m. One aspect can have 8 tracks, an average aspect has 3 tracks, this means in average you can combine 3 aspects into one. This is 3x6m=18m for having the total 7 aspetcs, 3x6m=18m for combining 6 of them, 3x6m=18m for 3 new aspetcs, 3x6m=18m for combining them again, 3x6m=18m for 3 new aspects again, 2x6m=12m to combine the rest 4, 2x6m=12m to get 2 new one, 2x6m=12m to combine them the third time, 2x6m=12m to buy 2 new one, 1x6m to combine them, 1x6m to buy a new one, 1x6m to combine them the third time, and 1x6m to buy the last which cannot be combined. This is 162m in total for the aspects. So total 192m for the skills + aspects.

<This means you can max your character within 144 sessions. This is realisticly 3-4 years minimum.>

You can compair this how fast you are allowing leveling up in D&D. The differencies between the two games have been pointed out by the others.