I am an older guy (I turn 60 tomorrow). I don't work so I have time to train as I see fit.

I generally ride between 70 - 100 miles a week with a partially loaded touring bike (tools, spare parts, extra layers of clothes). When I have a tour approaching, I increase my mileage about a month before departure. I begin adding more weight to the bike until I am riding my expected distance with a full load about 2 weeks before I leave. I feel I am ready when I can do two back-to-back days at my touring distance with a full load.