Explain the reasons, if any, for drawing a definite line in each of the following cases. Then further explain how this line can be drawn, if at all, in a reasonable way.
1. Minimum (or maximum?) age to drive a car
2. Minimum age to vote
3. Minimum age to enter (or be drafted into) the military
4. Minimum age to drink alcoholic beverages
5. Minimum age for election to the presidency
6. Maximum age before retirement becomes mandatory