some questions about S---N conditions

when i draw the diagram, i rarely make the "not S---> N" map. coz i want to keep the sufficient part is positive. for example, you cant serve as a U.S. senator unless you are at least thirty years old. in this case, i would like to draw " serve---> greater &equal 30, the contrapositive part is not less than 30 ---> not serve. but here is the thing,

 for this question

unles you get in an accident, you will live a long time

the right answe is : not live a long time-->get in accident

but for me, i d like to draw like this way:

live long---> not get in accident.

i know there is reasoning flaws here, but why this one has "not" onthe sufficient part?

thanks.