Well I don't see many people complaining that a 16 year old can't be a senator and I think that it's ok to limit that because in those ages we are still going through maturation and brain development so a senator below 25 (Iirc that's when brain maturation finishes) shouldn't exist because they could be inconsistent with their behaviour and ideology.

The real reason for someone to be worried about senator Vs normal people age is that even though a 40 year old can legally be a senator, socially we can see we decide to have way older senators and that's not a good representation of the population.

It wouldn't make sense to complain about senator age average not being close to young people if it's obviously not even possible for the average senator age to be lower than the age in which we are allowed to advocate for senator.