I'm 31. Some of the regulars on AVEN are older and there's a tendency for 20 year olds and younger to not stick around at all, but that's to be expected at a period of uncertainty. Much older members may not be accustomed to online communities nor know they're aro/ace spectrum. Some people just fall out of AVEN because of...well, you know, it's AVEN.
The age-internet problem will apply here too so we'll see a younger-than-average population too. I guess 20 - 30 would be average, maybe 25 - 30 soon?