I fall into this category of being a female follower who began leading in their 20s-30s, and yes, when I lead, I mostly dance with my female friends, and I usually only do so at my local milongas, or at lessons/practicas.
I think this phenomenon of female leaders dancing mostly with people in their own friend group or of their own age, it isn't that they are intentionally excluding others, I think it's in large part because of the challenges of inviting other women to dance: some women simply prefer to dance with men and will only target men with their mirada; women who might be open to dancing with women if they were asked, but who do not know you, will assume you're just a fellow follower and will not look your way when the tanda begins; even in my own community, people seem to forget that I lead - I think women at milongas are used to looking for men's eyes by default, me included, it takes conscious effort to look at the women as well (and to be honest, it's harder to do, as a follower you're doubling the number of faces you're considering now, so I don't really blame people for using gender as a shortcut to role).
Your odds of finding a partner are probably better if you're a woman who mostly or exclusively leads, but if you only lead for fewer than 50% of the tandas then it's going to be hard to find partners unless you resort to asking verbally. I also find that, as a woman of average height who is still working on stability when leading, I can't reliably dance well with any random follower, so at a milonga I try to find people I can attempt to give a satisfying tanda to, and that pool is pretty small. Sometimes there is a tanda I'd like to lead but I can't find a follower for it so I end up sitting it out or accepting an invitation from a leader instead.
Once in a while, if it's simple music and I'm feeling up to it, I'll take a chance on a follower who isn't one of my usuals, but it's quite risky. Many women, even if they accept a cabeceo from you, don't seem that eager to follow another woman, I can feel that their embrace is a bit shy, uneasy, nervous. I'm about average height and build for a woman, and many of them are trying to be super light, I assume that's because I look or feel fragile to them in comparison to the average guy (which is understandable). It takes time and effort to gain their trust, I have to strike the balance between dancing confidently or intensely enough to get them to connect with me and with the music, without going so far that I'll spook them and make them more nervous than they already are; sometimes that's a fun challenge, but that's why most of the women I dance with at the milonga are women I've danced with in group classes or practicas before, I don't want to make anyone feel awkward or self-conscious in a milonga setting.
So, in order to avoid awkward tandas, I am careful with my invitations. I try to invite by cabeceo unless they are a close friend who I know enjoys dancing with me, and since cabeceo rarely works on other random women I end up leading close friends almost exclusively. And then maybe people assume I only lead close friends, so they don't bother looking my way for an invitation, and so it continues... Maybe as we get more dual-role dancers, and those dancers become better dancers, people will change their habitual behaviour of seeking a partner of the opposite gender by default, but for the time being this has been my experience.
Also, just to mention, in my community there are plenty of 40/50+ women who are learning to lead or who have been leading for some years already, I'm actually one of the youngest and newest dual-role dancers around.