It's a stupid question because you can't assume anything. There is no average scenario. There's a best case scenario, there's a worst case scenario and 1,000 in between. At my last regional I would estimate 20% of captains were 50 or older! Sooo.... put that in your "average".

And "in this day and age" is NOT "in this day and age" five years from now, so no one can tell you an answer. I was hired and told that, "You'll upgrade in 2.5 years tops." Well it was six. While I would love to help you plan out your career and give you a better answer, all I can offer is advice: Find something else to do unless you have a four leaf clover birthmark.