Say you just start dating a guy, you go over to his house for the first time, and it turns out he has model kits displayed. Granted, they're more like a collection and look as though they haven't been touched in years. He explains that he hasn't barely touched them since before college, and doesn't play with them or have any intention of getting rid of them. Would this be a deal-breaker for you?
In response to the "why would it be" responses, I've always been under the impression that it was found "childish" for an adult to have model kits, be they cars, planes, robots, trains, or whatever the case is. As if models are on par with toys.
I think it'd be cute! I mean, I think the only issue I would have is if that's all you could talk about. Which is rarely the case with people. Because having a hobby you're obsessed with is sweet and all, but if you relate everything back to your models that could be annoying! (ex:: "Speaking of your aunt, I have this model...")