Two special elections to replace two older Senators, with the late Senator Lautenberg an especially significant case (he was 89).
I think I've written about Massachusetts before, but it's looking very much like a wasted opportunity. Ed Markey, the solid favorite, will turn 67 in July. That's not young!
The Republican in the race, Gabriel Gomez, is only 47 (he'll be 48 in August). So there's some hope of a relatively young new Senator. But I'll be pretty surprised if he wins.
In New Jersey, the only Republican in the race so far is Steve Lonegan, 57. It's looking as of right this minute that he's reasonably likely to win the nomination, but not be a very strong general election candidate at all in the October special, so the real question appears to be on the Democratic side. Three candidates there: Cory Booker, 44; Frank Pallone, 61; and Rush Holt, 64. C'mon, New Jersey!
By the way, it doesn't matter much in the long run, but for whatever it's worth the new placeholder Senator from New Jersey, is...48. Or maybe 47. He was born in 1965, says his newly-updated wikipedia page, and we have him as a 1987 Notre Dame grad, but so far no date of birth.