You start a list however you need given the context. It’s arbitrary.
As an example when doing time calculations in programming, UNIX time is the number of seconds that have passed since January 1st, 1970. If you needed a list ordered most recent to oldest, the highest number would be first.
To bring it back to you, a 100 is a better numerical grade than a 1. The alphabetical identifiers attached to grades are in reverse order to their numerical counterparts, which is even more fun because the person with the highest number and the earliest letter are considered “best.” However, in some card games (Uno for example) having the lowest number is best when determining score.