You hear lots of complaints that members of Congress are too old — in the Senate especially. What are voters doing about it?

At the beginning of the current Congress, the average age in the Senate was 62.9 years old. There's nothing wrong with having some older members stick around, but increasingly we're getting almost nothing but aged senators. It's not representative of the nation.

The issue is not the ones who stick around forever — such as Vermont Democrat Pat Leahy (currently 80, first elected in 1974) or Iowa Republican Chuck Grassley (86, first elected in 1980). Turnover in Congress is actually at healthy levels these days.

No, the problem is with incoming senators. The average age of new members elected in 2018 was 58.1 years old. That means a number of new senators are getting started when they're already in their 60s or even their 70s. Given that many senators over the years have said it takes a full six-year term to get up to speed, we're talking about people who will be in their 70s or 80s if they stick around for a second term. Of course, older politicians can still be highly effective. But the odds are that many of those who start their first terms when they're already senior citizens will eventually wind up being little more than reliable party votes rather than active legislators.

It's still relatively early in the 2020 election cycle, with several nominations still up for grabs; some contests that look potentially contested today will wind up being easy wins for the incumbent party. Still, it's late enough in the political season so we have some idea of what the field will be. I looked at the 26 candidates most likely to become new senators.

The average age of this group is about 54 years old, slightly lower than that for the previous incoming group (ages here are all as of Jan. 3, 2021, when the next Congress begins). The single most likely new senator, Wyoming Republican Cynthia Lummis, will be 66. Colorado Democrat John Hickenlooper (68) has a harder path to victory, but at this point he's still looking fairly likely to win his primary and defeat incumbent Republican Cory Gardner. Kansas will probably elect either Republican Roger Marshall (60) or Democrat Barbara Bollier (62).

And then there's Alabama. This is for the Senate seat that Jeff Sessions gave up in 2017, when he was 70. He was replaced as interim senator by Republican Luther Strange, who was 64. Strange was defeated in a runoff primary by Roy Moore, who was 70, after outlasting Mo Brooks, 63, to reach the runoff. Moore then lost to Democrat Doug Jones, who was 63 when he was elected in 2018 to the Senate. If Jones can manage to win a full second term, he'll be 66 when the next congressional session starts, but more likely he'll be defeated by either Sessions, who would be 74, or Tommy Tuberville, the former Auburn University football coach, who would be 66. Really, Alabama?

There are some younger Senate contenders. Democratic U.S. Rep. Ben Ray Lujan, who will be 48, is likely to be elected in New Mexico. U.S. Rep. Joe Kennedy III, who is now 39 going on 40, is facing Senate incumbent Ed Markey in the Democratic primary in Massachusetts. Neither of the two other younger candidates, Georgia Democrat Jon Ossoff (33) or Kentucky Democrat Charles Booker (36), are favored to win.

Add it up, and there will likely be more new senators who are 60 or older than those who are under 50.

Who is to blame? Mainly the political parties, at both the state and national level, who have a major say in determining congressional nominees. For whatever reasons — perhaps they're more risk-averse than they used to be? — the parties seem to gravitate toward older candidates. The most obvious case this time around is in the Colorado race, where Democrats had several viable contenders against Gardner, a weak incumbent, before the party successfully urged Hickenlooper to run.

There doesn't seem to be a big difference between the parties over the last 20 years. This cycle, the group of potential Republican senators I looked at are older than the Democratic crop as of now, but with several nominations still to be decided, it's too early to know how it will play out.

In recent years, for every Angus King (technically an independent, but he caucuses with the Democrats) who was 68 when he first became a senator from Maine, there's a Mitt Romney, the former Republican presidential candidate who was 71 when he was elected in Utah in 2018; for every Elizabeth Warren, the Massachusetts Democrat who was 63 when she joined the Senate, there's a Shelley Moore Capito, a Republican who was 61 when she was first elected in West Virginia.

It wasn't always this way. The average age of incoming senators in 1995, 1981 and 1975 was below 50 years old, and new senators who were 60 and up were relatively rare before the last 20 years or so. The Senate back then, before Majority Leaders Harry Reid and Mitch McConnell both increased the top-down influence of party leadership, was also a more active body, with individual senators far more likely to get things done on their own instead of just doing whatever their party leadership told them to do.

I can't prove that the two factors — relative youth and less party control — are connected, but my strong hunch is that they are. It's probably also not a coincidence that the parties likely didn't have as much sway over nominations back then.

I'm not talking absolutes. It's probably healthy to have the occasional senator who had a long career in some other profession and then entered politics, and that means having some older freshmen members. And sometimes a popular politician will, for any number of reasons, not reach the Senate until late in his or her career but still hit the ground running. Overall, however, we could use a lot more new senators in their 30s and 40s, and a whole lot fewer of those who are 60, 70 and up.

Jonathan Bernstein is a Bloomberg Opinion columnist covering politics and policy. He taught political science at the University of Texas at San Antonio and DePauw University and wrote A Plain Blog About Politics.