A Question About Ministry

I have been thinking a lot about this lately, considering my circumstance.

Does God call people to vocational ministry for a lifetime, a shorter time, or both?

I my denomination, ordination for a lifetime. I understand that all Christians are called to live a life of service to Christ their entire life. I talking about vocational ministry, or what is often referred to as pastoral ministry.

I have written about this before, here. I have known my share of pastors who are no longer pastoring, even though they would not be considered "retired." Most are middle-aged (late 30s to late 50s). Did God not call them for a lifetime?

I know for sure (beyond any doubt or second thought) that God called me to the ministry when he did. It was to serve as a pastor. I'm not doing that right now, and it's bugging me. I'm not dying to get back in the game.

This all sounds like the incoherent ramblings of weirdo, but that is where I'm at.