Jennifer Aniston is reportedly desperate to stave off the ageing process in an attempt to hold onto boy-toy John Mayer.

The actress has been splashing out $20,000-a-month on beauty treatments since hooking up with her singer beau, it's claimed.

“Jen is doing whatever it takes to hold back time - short of plastic surgery," a source tells the National Enquirer.

Apparently, Jen's quest for youthful looks involves private instruction with top yoga guru Mandy Ingber, and personal training sessions, at a cost of about $3,000.

She also pays a private chef $3,500 a month for organic, high-protein, low-fat meals.

“Jen is insecure about her legs, so she goes for anti-cellulite spa sculpting treatments twice a month," the insider claims.

"They cost $1,000 a session, but Jen swears that the sculpting keeps her skin supple and smooth.

"She calls the treatments 'necessary tune-ups."