Is it me, or are the majority of OEL creators under 25?

Yes. At this point in time, the pay is comparatively low and they're a lot of work. It requires someone who has the time to devote to it, and not much in the way of financial obligations like family, mortgage, health problems, etc. Which tends to select for younger creators. If the OEL movement takes off and more money gets put into it, the demographics should change a bit.