In maturity some soldiers see eye to eye (5)
I believe the answer is:
agree
'see eye to eye' is the definition.
(if two people see eye to eye they agree on things)
'in maturity some soldiers' is the wordplay.
'in' indicates putting letters inside.
'maturity' becomes 'age' (I've seen this before).
'some soldiers' becomes 'RE' (Royal Engineers).
'age' enclosing 're' is 'AGREE'.
(Other definitions for agree that I've seen before include "Go well together" , "Square" , "'Assent, concur (5)'" , "Accord, match" , "Have the same opinion" .)