Americans aren't eligible for a WHV (417), only a W&HV (462) and yes there is an option to extend for a second year but the requirements for a 462 are different from a 417.
"If you have worked in northern Australia in tourism and hospitality or agriculture, forestry and fishing you can apply for a second Work and Holiday visa."
The specific requirements can be found on immigration's website. Don't get information from other working holiday visa holders as the work and holiday is not the same visa.
https://www.homeaffairs.gov.au/trav/visa-1/462-
"If you have worked in northern Australia in tourism and hospitality or agriculture, forestry and fishing you can apply for a second Work and Holiday visa."
The specific requirements can be found on immigration's website. Don't get information from other working holiday visa holders as the work and holiday is not the same visa.
https://www.homeaffairs.gov.au/trav/visa-1/462-