The Constitutional requirement is: No Person shall be a Senator who shall not have attained to the Age of thirty Years "be a Senator", not "run for the Senate. Biden was born November 20, 1942, so he would be 30 before he could possibly "be a Senator". The Sec State of Delaware was correct, regrettably.
You're right; here the qualification for the position was, in the end, a function of time. The Delaware Sec. of State agreed to put an underage U.S. Senate candidate on the ballot in Biden's case, but Biden was old enough to take office by the time he was sworn in.
The California Sec. of State refused to put an underage Presidential candidate on the ballot in Eldridge Cleaver's 1968 case. I think he was 34 at the time, and I don't know if he have been the Constitutionally-mandated 35 years old by the time he assumed office, if he had won the election.
What I think is important here is that Cleaver had to show his birth certificate to determine whether he could get on the ballot. (I don't know for sure but I guess Biden had to show his also.) It's good precedent and I don't know if the courts will notice this.
Re: “What I think is important here is that Cleaver had to show his birth certificate to determine whether he could get on the ballot. (I don’t know for sure but I guess Biden had to show his also.) It’s good precedent and I don’t know if the courts will notice this.”
On what probable cause was Cleaver required to show it in 1968? Profiling? The norm seems to be *not* having to show it.