Link youtube account to my Google account

I have a YouTube account created on 2010, which is linked to a Gmail account. But I most used Gmail account is another one. I try to link that YouTube account to this Gmail. I read  several posts and I realize only the YouTube account prior to May 2009 can be unlinked and link to new Gmail account, reference:
http://support.google.com/youtube/bin/answer.py?hl=en&answer=183819

So I have to use two YouTube accounts.  As my current Gmail account is related to my AdSense, I plan to upload videos in this account.