My own personal experience is that I always look for the best candidate for the next 3-5 years. so, at 45 your age would be no concern. If there is a difference between a 45 year old and a 25 year old then it is the flexibility and eagerness to learn that a 25 year old often shows in an interview that a 45 year old does not. Often the younger person is eager and understands that they do not know it all and shows eagerness to learn. The older person often tends to imply that if the school did their job better then he would be able to be a better teacher. Both are probably correct....the 25 year old is eager to work with though. Although these are stereotypes and I was part of a panel that appointed a 59 year old woman to a NQT post last year as she was the best candidate.