Not old enough you would need to add 60+ years to all their ages for accuracy.
A clause needs to added to representation requirements that the representatives need to be within 5 years of the representees’ average age.
Apologies for the rant.
The average age in most electorates is going to be pretty similar, unless you start splitting them up by age.
So you're going to have representatives serving for one, maybe two terms - anyone staying longer is going to have to move to progressively older electorates each election.
Having them stick around for 50 years isn't great, but having a constant parade of brand-new mid-30s MPs isn't going to be any better.
Term limits. No more than the greater of two terms or ten years for any elected position. Forces there to be new faces, but does not discriminate against age cognitive tests should be required for all elected positions, at least at the state and federal levels, at least starting at whatever the medically accepted age where cognitive decline is more likely (or whatever the phrasing needs to be), and it needs to be yoked to whatever the medical science says, not a fixed age.
Ten years in any one position or ten years total in any elected position?
Career politicians have their downsides but for stability you do want a portion of experienced people. Governments comprised entirely of 'fresh blood' tend to be a steaming pile of garbage because no-one knows what they're doing.
Age quotas could be a reasonable solution, if you had an MMP or other proportional system involving members elected at large rather than every election being a direct election.
10 years for a particular position (governor, senator, whatever). So, you can be elected twice (or more for positions with short cycles), but then you have to move on. You can move on to another position, but you're ineligible to be elected for any position you've held for 10+ years.