David E. Kelley just might be the bravest producer in prime-time, network television.

Not because the only show he currently has on the air, "Boston Legal," is so groundbreaking or out-there. (As a matter of fact, Kelley regularly recycles plots he used in other shows, such as "L.A. Law," "The Practice" and "Ally McBeal.")

But because of who he has starring in "Boston Legal." More specifically, how long those people have been around.

In a medium obsessed with youth — both the people it puts on the air and the people it tries to attract for the sake of advertisers — "Boston Legal" bucks the trend. The big draw for tonight's episode (9 p.m., ABC/Ch. 4) — which Kelley wrote — is a love story of sorts featuring Shirley Schmidt (played by 59-year-old Candice Bergen) and one of her ex-husbands, Ivan Tiggs (61-year-old Tom Selleck).

And that's hardly an aberration on this series — the average age of the six actors whose names pop up in the credits at the top of tonight's episode is 53. (That's William Shatner, 74; Rene Auberjonois, 65; Bergen, 59; James Spader, 46; Mark Valley, 41; and whippersnapper Julie Bowen, 35).

Remember, advertisers (and, thus, network executives) are obsessed with the 18-49 demographic. And they're generally under the impression that viewers between those ages only want to watch actors between those ages.

It's a dumb theory all the way around, but it holds a lot of sway in commercial television. Which is why "Boston Legal" is so out of step — and refreshing.

Watching Bergen and Selleck together is a delight. The plotline itself is more than a bit wacky — Ivan asks Shirley to be the best man at his sixth wedding — but they rise above the sometimes loopy material.

Elsewhere, Auberjonois is great as his character, Paul Lewiston, meets with his estranged daughter (guest star Jayne Brook, 43). And Spader and Shatner continue to be one of TV's top acting teams as their characters, Alan Shore and Denny Crane, take on an assisted-suicide case. (The opposing attorney is played by Adam Arkin, 49.)

Kelley and the other writers seem to have more trouble coming up with stories for the young characters than for the older ones. Ryan Michelle Bathe, 29, seems to have all but disappeared, and the best storyline Justin Mentell, 23, has had in months has him matching wits against the recurring character played by Betty White — still going strong at 84.

Hey, Joanna Cassidy, 60 (who's not in this episode), has popped up regularly as Denny's very sexy, tough, much-married fiancee. Even Michael J. Fox, who recently completed a multiple-episode story arc, is no spring chicken anymore at 44.