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.
They definitely have not looked up how old he is, so I’m going with the latter and they thought this was a dig at Biden.