People ask all the time "Can I ride a century?" And the normal response is something along the lines of "Well, if you can ride a metric century, then you can ride a century!" So with that kind of thinking, get to riding, and see how you feel 5 weeks from now. Go ride some 100k or 125k rides, if you finish and feel okay, there you go, and if you're doing a deathmarch at 50 miles, reconsider. Ride your own pace, don't worry about keeping up with somebody riding faster than you.
I am persuaded that there are athletic young people that have never ridden a bike that hop on one and ride faster and farther than I can, by the way.
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"be careful this rando stuff is addictive and dan's the 'pusher'."