substr the the_author_meta

I want to substr the result of the_author_meta(‘user_registered’), but the function does not echo, so I cant
Is there a way to do it?

This is how im doing it, but does return an empty value
$aaaa = substr(the_author_meta(‘user_registered’),0,4);
$mm = substr(the_author_meta(‘user_registered’),5,2);
$dd = substr(the_author_meta(‘user_registered’),8,2);
echo $aaaa $mm $dd
also if i define the_author_meta also returns empty

Thanks