First a disclaimer: I'm the co-author of one of those pesky books about co-sleeping that your husband doesn't want to hear "evidence" from. I can tell you first-hand of the hundreds of parents who told us about how their children eventually left the family bed. (We have a whole chapter on moving beyond the family bed when the time is right. It's called A Farewell to Arms...And Legs...And Feet.) I can tell you that many parents have found that 3 or 4 or so seemed to be an excellent age to help guide a child into a more independent sleep situation. Some left way earlier with little fuss. Others later. (So much depends on temperament.) The ones who remained significantly later usually had parents who didn't do anything to encourage them to sleep on their own. But since your DH doesn't seem to want this kind of info (sounds like he's had a bad experience with parenting books; I understand.), here are a few brief anecdotes -- not from the book, but from my life and from a few of my friends -- that might help your situation. Maybe you could just copy the next few paragraphs and print them out separately so he doesn't know they're from a book author!
My own daughter left our room when she was 5. She'd had her own bed in our room since she was 2, but space constraints in our little San Francisco house (where we have our small home office) precluded us from being able to let her try out a room of her own. We were thinking seriously about how we'd have to build another room for her, but one day she discovered that a decent-sized closet in another room has a window and a beautiful wood floor, and exclaimed "Mama, this could be a room. This could be MY room!" You've never seen a mama clear out a closet as fast as I did. We made it a magical hideaway, very much like the sweet little lighthouse room in Rosemary Wells' book "The Island Light," and she has slept blissfully in there since. (Except for the night when I was out with a girlfriend and my hubby let her watch Matrix! Ergh...) Ironically, it's her non-family-bedded friends who seem to frequently end up in their parents' beds!
A friend's child has been sleeping happily in her own bed since she was about 2. No crying it out, just a kid who slept well to begin with and decided that the new toddler bed was very cool and so was the scented pillow her Mama put on it when she slept there.
Two other friends were able to gently "nudge" their children to sleep on their own when the children were around 3 or so.
Another friend's child joined her sisters in their room when she was 2 1/2.
Bunk beds were the answer to a couple of other friends' desire to move their children out of the family bed at the ripe old age of 4.
I could go on and tell of the hundreds of tales we heard while compiling the book, but those are book-related, so I won't!
I hope these help! Good luck with your situation.
Co-author, Good Nights: The Happy Parents' Guide to the Family Bed