The entire point of the Senate is for older more experienced politicians who know what they're doing more so than the House Reps

I understand the point of the Senate.

and replacing them with a bunch of 35 year olds defeats that purpose. A normal person can't retire until they're what, 65? (And that's gonna go up when the GOP gets its way and "reforms" social security)

I m not advocating throwing out the entire senate and replacing them with 35 year old's. Democrats do need older experienced members in the Senate and in leadership. It helps when votes on the ACA come up. However It becomes a problem when so many blue state Dems park themselves in the Senate and refuse let the next generation move up. ( I m looking at your Dianne Feinstein). Yes having experienced members is good but having too many older ones is a problem.

Many presidential candidates are picked from the Senate. There aren't as many options when a majority of members park themselves in the Senate and refuse to let the next generation move up. Having some blue state Democrats retire and replaced with 35-46 year olds would sure replenish the bench come election time. Not all of them have to retire but some of them should for the good of the party. Had more of them retired sooner, we would have had more potential options in 2016.

I assume you also thought Bernie Sanders and Hillary Clinton were too old to be President?

In an ideal world we would pick the most experienced member of Congress to become President. In reality Democrats do best when they nominate younger charismatic candidates. Yes I do think Clinton and Sanders were too old to be President. A 70+ year old candidate isn't my ideal first choice for President. A 70+ is going to have a harder time advocating for hope and change. The ideal age is 46-54 for candidates.