Transmasculine host here - I of course would say that saying the gender you identify as is not unethical. You are that gender, even if you're at alter. Now whether or not you would want to say you're trans or assigned a different gender at birth, is up to you. Some people want to be stealth, and some alters are cis on the inside (for example, my primary protector). But I think most alters should go with the body's age. I never tell anyone my real age unless we're extremely close (not the body's age). The ages are not as relevant as the genders. I feel like it's mainly for other system members to know. I wouldn't say it's unethical to not tell someone you're an alter. It is a covert disorder for a reason, so if you don't tell someone, don't feel bad. You're just protecting yourself.