There's a lot of goog advice above.
My tuppance is to inspect the frame (typically around the BB, head-tube and seat cluster) and if all good build
and ride. While I'm not a fan of AL, I have to admit some of my longest day trips (+200 km on mixed paved
and unpaved) have been on old AL. There is something about AL that makes you feel that every pedal stroke
is going to the back wheel.
