I don't know what the metrics are that determined the above, but Biden would be too old by 2024, heck he is too old now IMO.
He was the right man for the right time and is doing a fantastic job, but I am sure the Democrats must be able to find some one else to carry the fight.
Of course if trump gains the nomination , I am sure Americans will not have another round of tramp drama, I cant belive that the country is so fare gone that would elect trump again.