Fixing some stuff with the welcome message

i didn't like how before, if you put anything other than a 0 or 1, then
the program wouldnt do as you expected.
i now make it more explicit. you have to enter 1 for Aging/Preemption
and anything else will give you no aging/ no preemption.
this is a small change, so if you guys dont like this, im ok if you
reject