Rod Stewart walking down Beverly Drive with his wife Penny Lancaster and their child Alastair Wallace Stewart. Beverly Hills, California - 26.01.08

The Maggie May hitmaker and model Lancaster are desperate to add another child to their brood - but their efforts have thus far proved fruitless.

And Stewart, 63, concedes his age may be preventing him from becoming a dad for the eighth time.

He says, "Trust me, I am trying my very hardest to have another child. But I am not quite Superman like I used to be. I am in my 60s now."

But Lancaster disagrees: "He's lying, he is Superman."

The couple have one child, two-year-old son Alastair Wallace.

Source: WENN