Taking a few older applicants spreads the retirements out and avoids a block on upgrades as no one is leaving, followed by a large number of departures at the same time, putting a strain on training capacity as a high number of promotions will happen close together, which then also requires a new first officer to be brought in as a replacement.
A large number of junior captains and new first officers also gives rostering difficulties as they can’t be paired together. Overall experience heads south and insurance premiums may rise.
When Virgin Blue first started, they put second hand engines on some of their aircraft to avoid having serviceability disruptions and a sudden major expense which would happen if they all came due for overhaul at about the same time.
An older applicant brings experience into the company, is more likely to stay long term and spreads the age demographic out . This may compensate for the reduced return of service, difficulty in teaching an old dog new tricks and greater sick days.