Link for anyone interested in purchasing the official fan book
Alternatively, you can read all the scans here (press left/right keys on the keyboard to move between pages)
According to age Akame's 10!? O.O
Actually, she is between 10-19. No additional info is given. Very few characters have actual age stated. Most just have their generations.
It actually wrote 10代 which is 10's/teens and 20代 for 20's. The 20's one has it a bit more detailed compared to the teens.
This is what the symbol mean:
代 - Decade,
代前半 - Early decade,
代中半 - Mid decade,
歲 - Actual age,
歲付近 - close to age.