By BILL BARROW
Associated Press

HOUSTON (AP) - Democratic presidential candidate Joe Biden is shrugging off thinly veiled criticism from younger rivals suggesting he is too old for the Oval Office.

The 76-year-old former vice president told reporters Friday he'll prove his fitness through the campaign, and he pledged to release his medical records after his next physical exam.

He didn't say when that would be but promised it would come before the Iowa caucuses in February.

Another presidential candidate, 44-year-old Julián Castro, used Thursday night's debate stage to suggest Biden had forgotten details of his health care proposal that he'd just discussed.

Fifty-year-old Cory Booker added after the debate that there are a "lot of people who are concerned about Joe Biden's ability to carry the ball all the way across the end line without fumbling."

Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.