Janeane Garofalo claims to be asexual. That’s what it says in her Wikipedia entry. It’s also what she says at 18:15 in this YouTube video:
At 20:25 in the same video, there’s a minute or two about the claim that Morrissey is asexual, as it says in his Wikipedia entry:
In each case, though, it appears that they weren’t claiming to be asexual their whole life, just some significant proportion of it.