Board Thread:Manga/@comment-86.100.245.104-20151024221304/@comment-26207277-20151026080739

A brief recap:

Eren was 9 when Shingashina's gate and Wall Maria's gate were destroyed (year 845). From then till 847, he worked on the farms (age 11-12) and trained for 3 years as a trainee (age 14-15). Then 3 months have passed since they have graduated from up to the current chapter. So Eren is around 15 or 16 currently in 850.