Model building? Go to your local hobby shop and buy him a pre-painted, snap-together Star Wars kit. (That way, you can avoid having to buy paint and glue, which can cost as much as the original model did.)
If it takes root, well, there are clubs and websites and message boards; it can be as social or as reclusive a hobby as he wishes.
I know it’s not quite along the lines of what you described but I saw this recently and thought it would make a great gift for any fan. Kinda takes the sting out of paying for stuff too.
We have one kid, but she is almost 3 at this point so we’ve done the Mother’s/Father’s Day thing a couple of times now. But no matter what the gift giving situation is next year I’d still like to put in the effort to make his celebration memorable this year the same way he did for me.
Start with a jigsaw puzzle and see how compatible/competitive you all are. Also give him something you know he enjoys, and sex. They like sex.
What sort of computer games does he like playing? It might help us come up with some potential hobby/gift ideas.
Really? Mine has mysteriously become three years old, too. How does that happen?
It’s an epidemic! It happened to mine last month.
Seabreacher.
Just sayin’.
Kites. Kites are good.
Buy him a 3D printer so he can literally make whatever he wants (that’s not bigger than the printer)
Don’t mean to be rude here, but choosing a hobby for your husband is not going to work. Unless you know he is in to it, chances are very likely he will be disappointed with whatever you pick, especially if you choose crocheting (seriously??).
I think you would be better off planning a weekend getaway or tickets to something he really likes (concert, sporting event, etc).
How about a balsa wood model plane kit? They are very intricate and if he is a detailed kind of guy it takes a good craftsman to build them correctly.
Or an easel and some paints… who knows maybe he is the next Gauguin or Jasper Johns.
He asked her to pick a hobby. Part of the fun can be trying new things out together and deciding what works and what doesn’t.
My BIL and my sister (his wife) used to design needlepoints together and do them together. He’s a dentist, so likes working on small intricate things, and she liked needlework and art. They enjoyed it together, because they enjoyed being together. Don’t fount out nontraditional activities if the goal is exploring new hobbies.
I showed this to my husband and his response was, “FIND OUT HOW MUCH THAT IS!” To which I responded, “You will totally end up dying in one of those things.” That caused him to yell, “I WANT TO DIE IN A SHARK SUBMARINE!” 
Unfortunately these are so expensive they don’t even list a price on their website so this isn’t going to happen, but knowing such a thing exists makes him very happy.
Genealogy?
Actually I like to take pictures of trains from a plane. A model airplane or helicopter with a camera would be a lot of fun.
It’s probably not as sexy but what about a subscription to MAKE magazine? It doesn’t focus on any particular hobby so he could chose his own. I will warn you that it could be dangerous; my sister started getting me MAKE for my birthday and I’ve ended up making all sorts of whacky things. 
That does sound like fun. Hellishly difficult to control though I bet.
How about something like these UK schoolkids did:
Cheesemaking
LEGO. You never outgrow it.