I seem to remember it being 60 average for TL not 61, I could be wrong though, But remember many rounds although ranked don't count towards your average or tier progression, Those being any custom CC course, par 3 or par 5 courses,
I found this a few minutes after I made my post.
- When you have played at least 500 ranked rounds - and your average score is equal to or lower than 60 you go from Legend to Tour Legend
I think the 500 ranked rounds have been increased since that post was made but the average is still correct.,