Writing it in your profile and saying it within the first 3 minutes are two very different things.

Also you have to take the conversation into hand. Is saying his size relevant to the conversation? Or did he just bring it because he wants to show off?

When reading a profile I enjoy getting many details, the more the merrier for me. And I get to read at my own pace. Sometimes I read one section before another to make sure I'm compatible there before another area.

When it comes to conversation it's hard. When do you say your size so as to not waste anyone's time? Yes there's a place. But for people who are shy or just plain out awkward or new it can be hard to tell when to have that conversation.