I mean, this does create the obvious question - "If Biden is too old to run for President, isn't he too old to be president? Doesn't he care about the safety of America [blah blah Fox News talking points blah]"
I personally think it's fine because the job of President mostly gets done by the team of staffers around the White House, but we'll need a good answer for that question when a reporter asks it
It won't satisfy the likes of Trump or Mike Johnson, obviously, but "enough energy to be president for six months" and "enough energy to be president for six months and simultaneously run a presidential campaign capable of winning" is not a particularly difficult distinction to draw, IMHO.