Confused about Gundam panels

So I visit anime conventions and what I see in the convention panel books are Gunpla 18+ and in general Gundam Panels 18+ and I'm wondering wtf how does making models of Gundam kits I see online or in Akihabara have anything to do with being 18+? I 'm assuming it's no different than any other model car, plane, tank that gets made so how does it evolve into being 18+ or does it because the panelist just wants to cuss a lot? Thanks. Really I can only imagine it going ahh shit I painted the damn arm wrong color of white. idk. Help?

I remember going to a "What's wrong with x" panel that was 18+. I asked them and they said it was marked 18+ for language because they were going to swear a lot and it wouldn't be safe for children's ears.

Wow ok. I think it's silly that someone can't do a Gundam panel without cussing lol. I'm going to a convention next month and looking through the schedule I see yet another 18+ Gundam panel (I never been just see them all the time) so it was something I just had to ask.