Deidara was 18 at the end of part 1.
Track back 7 years prior to that orochimaru left akaskui and deidara was 11.
3 years ? That is an assumption and we don't need assumptions we need facts.
Itachi was 18 at the end of part 1.
We know at age 13, he was promoted to the rank of Anbu captain and then went on to commit the uchiha massacre.
This leave a five year gap in which he could of recruited deidara making deidara 13 at the youngest not 10.
The page you used is an obvious translation error once you add up the math.