AS a businesswoman, full-time mother and actress, Liz Hurley might seem like she has life well and truly sorted out.

But the star has confessed that she feels "like a real lunatic" since turning 40 earlier this year.

"I felt completely different," she said. "I formed a company for beachwear just as my family was saying: 'Well you've done quite well with your lovely home in the country and your baby, so we guess you'll be quietening down now', but I just went into lunatic mode."

Liz isn't the only celebrity feeling agitated about her age. Thirty-one-year-old Robbie Williams also dreaded the transition into his 30s

"At 29 or 30 you start going: 'Who am I? What have I done? Does it mean anything? Do I mean anything?'," he said.

While for some, milestone birthdays are all about balloons and birthday cakes, for many people hitting 30, 40, 50 or 60 can cause a life-changing jolt, says Bill Bytheway, a leading researcher on age and birthdays.

"Some people find that their lives change radically upon reaching a birthday," he said. "How old you are is one of the most commonly asked questions.

"Many of us have strong views about how people are supposed to behave given their age. We are a more numerate society and have become more sensitive to ageing."

And while some of us delight in the inkling of a surprise birthday bash, others shudder at the thought.

"Most people like to be made a fuss of, they like to be remembered and have a special day," said Mr Bytheway. "But they don't like growing older and don't like to be reminded that it's happening.

"Most of us don't like big surprises because we don't like to feel things are getting out of control."

So if you're about to mark a milestone age, here's some tips to surviving it in style:

AGEING POSITIVELY

l If you don't want a surprise party, organise one for yourself - that way you stay in control.

l Remember milestone ages are like a New Year or having a new diary. You can start with a clean sheet and anything is possible in the new decade.

l Use it as an opportunity to stop, think, and take stock.

l Celebrate what's happened in your life and clarify what you're going to do in the future.

THRIFTY AT 30

The hedonistic days of your 20s are behind you, and for many reaching 30 is considered a time for really taking responsibility.

"Turning 30 is a time of reassessment," says Steve Errey, a coach specialising in personal growth for 30-somethings.

"Our 20s are a blur of career, money, fun, friends and relationships, and as we head into our 30s things tend to change.

"People see the rest of their lives stretching out in front of them"

FUN AT 40

They say life begins at 40 - and life coach John Rushton would agree.

"Forty really is an age where life does begin for some," he said. "Children have grown or are growing up, your home is secure, you have a car, you've seen life and have a more stable group of friends.

"Hopefully you are more able to cope and get by better in life."

FANTASTIC AT 50

At 50 you've hopefully secured your finances and are starting to enjoy life in the way you would like to, said Mr Rushton.

But he added self-perception could affect the way you feel about hitting the big 5-0.

"If you think where you are now is a good point to be you will be more inclined to celebrate," he said.

SPARKLING AT 60

For many, celebrating 60 can be difficult. It marks the beginning of bus passes and OAP status. But Mr Rushton argues that entering your 60s marks a new beginning.

"Provided their pensions or saving are adequate, many people at 60 start to live all over again."

LIFE REALLY DOES BEGIN AT 40

Mike Nolan, assistant news editor at the Worcester News, tells why he was quick to celebrate his 40th.

"Having turned 40 in the past couple of weeks I must admit this does feel like a landmark age.

"However, I can't say I have let it worry me and I don't fret on the passing of the years.

"I suppose at a landmark birthday you look back on life and especially the previous decade on what has been achieved and assess how happy you are with your lot and you can get a little nostalgic.

"In my 30s I have changed career, lived away from my native Midlands for a couple of years for the first time, met and married my wife, became a father and am now on my second home with my family.

"I haven't become a millionaire entrepreneur yet but I suppose that is the goal for the next decade.

"I am certainly more conscious of what I eat and drink and do occasionally worry that I must do more to keep fit.

"I must also admit latterly to becoming a bit of a grumpy old man and do sometimes despair at what I see happening in society.

"I probably act more like 70 when I'm off on one.

"But, all in all, if you are looking for a mid-life crisis expecting me to buy Just for Men and find me chasing 19-year-old girls forget it. I'll accept ageing gracefully."