I think 40 is still giving a lot of grace time. I'd say mid 20s. Until you're nearing retirement. If you can collect benefits at 65 1/2, then you can start with the half years at 63 1/2, but only in the context of retirement, or other things where 65 1/2 is relevant. Otherwise you're wasting precious moments, heartbeats, and breaths on unnecessary nonsense.