In a YouGov poll conducted between July 25-29, 59 percent of Republicans surveyed said they would prefer a president under the age of 75. Trump celebrated his 78th birthday in June. Forty percent said they had no preference, and just two percent said they would prefer a president over the age of 75.
He was pressured to step down and then was ultimately willing to listen and do so. There was no method to force him to step down – he had more than enough delegates locked in to win the nomination if he wanted to keep going.