It it clear that the system is not now maintainable? They assigned a younger engineer to work with the man, and "impossible task" could be an exaggeration for "

It it clear that the system is not now maintainable? They assigned a younger engineer to work with the man, and "impossible task" could be an exaggeration for "difficult" or could mean "never as good as the original guy", both of which are different from "he can't do it."