if you've not ridden a bicycle for years, the first thing you notice is this: you really don't forget how to ride it. the second is: am i really this unfit? then there is all this stuff about chains falling off, tires pumping out, blood blisters from the chain (when it comes off and gets jammed in the cogs), and what generally comes together as this is way too much work. there is none of that skipping through the traffic, through cars, roads, footpaths, back trails, not at first.
grease will line your hands and fingers, dig into the side of your nails, and no amount of washing will get rid of it.
the question you will ask is, why bother? why do this to yourself? and the answer will be simple: can you seriously be defeated by a bicycle?