In the poetry world, there are plenty of late starters, people who relatively late in life start to take their writing seriously, in performing it, or trying to get it published. I'd include myself in that category, to an extent - I only really started to make a big effort about eight or nine years ago, although I'd dabbled in a rather directionless fashion for years before that.
There are also, though, plenty of poets who write and are published right from their teens, who maybe do English and/or Creative Writing at university, but who don't publish a full collection until well in their 30s, maybe their 40s. I've come across quite a few lately, in fact I'm reviewing a couple at the moment, and I have to say I admire their patience and dedication in resisting the urge to put out a debut collection until they're ready. I can think of a couple of problems that the long wait can create, but for the most part they seem to sidestep these rather admirably.
I'd guess that the rise (or rather the resurgence) of the chapbook has something to do with it, too. It means that poets are able both to get their name out there and to plan and create complete, self-contained pieces of work. Some put out several pamphlets before ever even considering submitting a collection. From what I've seen (someone like Helen Mort might be a good example), it's a thoroughly good thing, allowing younger poets to experiment with voice and form.
I'm rambling, I know. But I'll try to put these thoughts in a more coherent form soon...