Some Hillary supporters use Bernie's age as an argument against him all the time. Hillary frankly speaking isn't much younger.
Coriolanus is not a Hillary supporter (he's a Corbyn supporter) and Coriolanus's post was explicitly not about anything having to do with preferring one candidate to another. His point is just that Bernie, at 74, can't really afford to wait around for midterms to rile up the base in the way most useful for the Democratic Party.
I do think there's a pretty meaningful difference between 68 and 74 when we're talking about an 8-year term in office, but I agree that they're both too old for the job really. But you can wait for somebody to actually make the argument before arguing against it!