pair wont go in box...why?

[ush2611]

hi, i know its been mild but is it still too early for nestboxes...i have one adult pair..that i bought this year, i put the box in two days ago, out of curiousness really and thought the hen might go straight in, but neither of them have gone near it...they are not rung, so im wondering if they are in fact past their best...he has his ring, so i dont think hes a juvenile...i was told they were from 2008...wandering if they havent gone in because for them its a little early in the year??