Age is a valid concern. It was brought up when Reagan ran for his second term and when Biden ran in 2020. Trump, only a few years younger, is now older than Biden when he ran in 2020.
Trump also shows signs of the same cognitive decline they accuse Biden of. He confused Pelosi and Haley, he confused Obama with Biden, called Orbin the ruler of Turkey. He has been slurring his words in recent speeches. He has shown other signs of what could be
incipient dementia as well.
Of course all of this is based on online speculation, not medical diagnosis and the effects of aging are highly variable. You can have 80 year olds sitting in nursing homes or 80 year olds out running marathons and writing scholarly articles. But the lack of any self awareness in the MAGAverse is ironic.