A year in a dog's life is supposed to be equivalent to seven in human terms. On the way to interview Christina Aguilera, it crosses my mind that there might be a similar exponential growth rate at work for diminutive blonde pop starlets. For how else to explain that, at the grand old age of 27, Aguilera is releasing her greatest-hits album? Don't most people take, well, at least a few decades to accumulate enough material? Isn't it the sort of thing aging artists do to make themselves feel better when they're in their fifties, to remind their fans of a halcyon era before they were destroyed by the gradual onward march of time and deep-fried peanut butter sandwiches?

It doesn't help that Aguilera looks so extraordinarily youthful and tiny in the flesh (what little there is of it). When she walks into the London hotel suite where we have arranged to meet, her head is almost entirely swallowed up by a large leopard-print hat with a brim that seems to cast a shadow over her whole face. A big diamond-studded silver pendant hangs loosely round her neck. Her lipstick is a pale frosted pink and her 156-cm frame has been noticeably augmented by a pair of extremely high black patent stilettos. She gives a small smile and shakes my hand so gently it feels as if her wrist might fall off on to the patterned carpet. The whole impression is that of a little girl playing dress-up in her mother's wardrobe.

She doesn't really go for the canine seven-year theory when I put it to her. "Yeah, it's crazy," she says, looking at me slightly oddly. "It's been quite the journey." Certainly Aguilera seems to have been born with the kind of precocity gene that makes Shirley Temple look like a late developer. She was performing in local talent shows at the age of 6. Her first television appearance, as a contestant on the long-running U.S. series "Star Search," came two years later. When she was 12, she landed a presenting job on the Disney Channel's "New Mickey Mouse Club" (her contemporaries included Justin Timberlake, the actor Ryan Gosling and fellow blonde pop poppet Britney Spears). She was 17 when she released her first single, "Genie in a Bottle," which went straight to the top of the American charts and stayed there for five weeks. That means that although she is still three years shy of her 30th birthday, she has nonetheless racked up 19 years' worth of professional experience.