Country music legend Willie Nelson has kicked off his eighties by challenging Sir Ian McKellen for the role of Gandalf in director Peter Jackson's The Hobbit movie trilogy.

The singer/songwriter, who turned 80 on Tuesday (30Apr13), has shot a spoof audition tape for American chat show Conan, in which he acts out as the fantastic wizard while smoking a joint.

Nelson, a long time advocate of marijuana use, offers up lines like, "Hey, look at that dragon!" and "Thou shall not pass an unlit joint, man... That's just not cool."

And he ends the skit with a message to Jackson, stating, "You can hire me and fire that Ian MCKellen guy. He's a good actor but, hell, I'm Willie Nelson."

The thespian has seen Nelson's audition tape and responds, "Dear Willie, You are far too young to play Gandy. But nice try; have a stoner of a birthday. Love and admiration."

Meanwhile, the old-timer's birthday also falls on the same day as the release of Kenny Chesney's new album, Life on a Rock, which features Nelson collaboration Coconut Tree.

Chesney tells Country Weekly magazine he had a chance to celebrate his pal's 80th birthday early, revealing, "Over the holidays, I went to Hawaii and sat around a poker table with Willie for a couple of days. And trust me, we climbed our own coconut tree. It was a lot of fun."