I figured out I'm trans at age 15, and only briefly/casually talked about it with my mother at that point but without making it a clear "coming out" before I went back into the closet again. I mostly just vented some thoughts about it, like expressing a curiosity. Her not taking it even remotely seriously and trying to talk me out of it, was half the reason I went back to the closet and went into denial.
At age 19 I came out for real, first to my best friend. She said she didn't know but thought it made a lot of sense, and was instantly supportive and accepting. We've known each other since we were toddlers and been best friends since we were 12. So I kinda knew she wouldn't ditch me over that and I was right.
Then I started coming out to my mother (again?) but I didn't say it all at once. Rather, I slowly eased her into it and made it a several months long discussion that lead up to a clear coming out eventually, instead of a single statement and then discussion. She was reluctantly accepting of it, but struggled to understand why transitioning was important for me, and she's been very ambivalent and hard to read about it. It took her a lot of years to come around and only stopped using the wrong name/pronouns after 7 years, which was about 2 years ago now.
I let her spread the news to my father and sister as I couldn't quite stomach more coming out at that point and I appreciated her taking some of that burden off of my shoulders. My father wasn't happy about it, but very passive aggressive and silently disapproving. He's still not liking/understanding it, but seems to accept it better now. My sister was the most supportive of my family members.
Then I also let my best friend spread the word about me being trans to our friends in common, so I didn't have to do even more coming out, after I had come out to my school class at the time as well. So I took a very lazy approach to it, which was very neat at the time but... at this point I've no idea just how many friends of friends of friends of her's, mine, my family members and whoever just know about me being trans cause someone else told them. The "outing" was spread like a wildfire! It doesn't bother me all that much though, if people out me or not.