As a Japanese person living in Japan, I can tell you that the bokukko phase eventually comes to an end. I wouldn't be able to take any girl/woman seriously who is over the age of 16 if they refer to themselves as boku. Obviously, I wouldn't be so mean as to say "don't fucking talk like that you sound stupid," because, hey, whatever floats your boat.
I'm a guy in my 40s but I still say boku because it's just a friendlier (if not kinda dorky) way to address myself.
This aspect of Japanese is quite contextual though. In Okinawa, where I live, it's pretty common for even adults to refer to themselves by name amongst friends and family, which is something only toddlers do in mainland.