The North Dakota Constitutional Amendment passed yesterday with a 61% Yes vote (a majority vote was needed) that bars candidates for US House or US Senate who would attain their 81st birthday by December 31 of the year preceding the year in which their term ended.
So, this could stop some people who are younger than 79 years (for US House elections) and younger than 75 years (for US Senate elections) on Election Day from seeking office.
This will likely face legal challenges based on the US Constitution and prior rulings that qualifications for federal offices cannot be more than those stated in the US Constitution (e.g., the US Term Limits decision of the US Supreme Court).