I found this info on the FAQ section of this site:

After you make 45 posts or more, custom avatars become enabled for you, which allows you to upload an avatar image from your computer.
That is wrong and out dated information. When I went around the site looking through threads and what not, I found people saying the standard number of posts were 15, or 25, or 30, etc. etc. It just confused me

As you can see from my avatar, I found and was told by one person that 10 posts seems to be the current standard. I feel that correction should be made soon. Though I can understand why it's been over looked when there are bigger and higher things to deal with.

This may be on the insignificant side and may be a minor detail, but it's the little things that are often the biggest pains.

Take care