For me reputation is inherent, why exclude a user who has just arrived at steemit or who has been posting for a short time?

If you do that what you will achieve is that new users do not have confidence and credibility in steemit, what could be implemented is an identity verification for those who make life in the weekly challenges, is my humble opinion on the matter.

One method of verification can be a short video in which the user states his or her name, the date he or she joined steemit and the reasons why he or she is participating in a certain challenge.