WE all accept that getting older is inevitable, and now leading clinicians have revealed the exact age when different body parts start to decline, most alarming being the brain and lungs.
French doctors have found that the quality of men's' sperm starts to deteriorate by 35, so that by the time a man is 45 a third of pregnancies end in miscarriage.
Here, with the help of leading clinicians, Angela Epstein tells the ages when different parts of the body start to lose their battle with time.
BRAIN - Starts ageing at 20.
As we get older, the number of nerve cells - or neurons - in the brain decrease.
We start with around 100 billion, but in our 20s this number starts to decline.
By 40, we could be losing up to 10,000 per day, affecting memory, co-ordination and brain function.
GUT - Starts ageing at 55.
A healthy gut has a good balance between harmful and 'friendly' bacteria.
But, levels of friendly bacteria in the gut drop significantly after 55, particularly in the large intestine, says Tom MacDonald, Professor of Immunology at Barts and The London Medical School.
As a result, we suffer from poor digestion and an increased risk of gut disease.
Constipation is more likely as we age, as the flow of digestive juices from the stomach, liver, pancreas and small intestine slows down.
BREASTS - Start ageing at 35.
BY their mid-30s, women's breasts start losing tissue and fat, reducing size and fullness.
Sagging starts properly at 40 and the areola (the area surrounding the nipple) can shrink considerably.
BLADDER - Starts ageing at 65.
Loss of bladder control is more likely when you hit 65.
Women are more vulnerable to bladder problems as, after the menopause, declining estrogen levels make tissues in the urethra - the tube through which urine passes - thinner and weaker, reducing bladder support.
Bladder capacity in an older adult generally is about half that of a younger person - about two cups in a 30-year-old and one cup in a 70-year-old. ....
LUNGS - Start ageing at 20.
Lung capacity slowly starts to decrease from the age of 20.
By the age of 40, some people are already experiencing breathlessness.
This is partly because the muscles and the rib cage which control breathing stiffen up.
VOICE - Starts ageing at 65.
Our voices become quieter and hoarser with age.
The soft tissues in the voice box (larynx) weaken, affecting the pitch, loudness and quality of the voice.
A woman's voice may become huskier and lower in pitch, whereas a man's might become thinner and higher.
EYES - Start ageing at 40.
Glasses are the norm for many over-40s as failing eyesight kicks in - usually long-sightedness, affecting our ability to see objects up close.
HEART - Starts ageing at 40.
The heart pumps blood less effectively around the body as we get older.
This is because blood vessels become less elastic, while arteries can harden or become blocked because of fatty deposits forming on the coronary arteries - caused by eating too much saturated fat.
The blood supply to the heart is then reduced, resulting in painful angina.
Men over 45 and women over 55 are at greater risk of a heart attack.
LIVER - Starts ageing at 70.
This is the only organ in the body which seems to defy the aging process.It is the most trust worthy of all our organs.(So do not damage it at least with your deliberate actions !)
KIDNEYS - Starts ageing at 50.
With kidneys, the number of filtering units (nephrons) that remove waste from the bloodstream starts to reduce in middle age.
PROSTATE - Starts ageing at 50.
The prostate often becomes enlarged with age, leading to problems such as increased need to urinate, says Professor Roger Kirby, director of the Prostate Centre in London .
This is known as benign prostatic hyperplasia and affects half of men over 50, but rarely those under 40.
It occurs when the prostate absorbs large amounts of the male sex hormone testosterone, which increases the growth of cells in the prostate.
A normal prostate is the size of a walnut, but the condition can increase this to the size of a tangerine.
BONES - Start ageing at 35.
'Throughout our life, old bone is broken down by cells called osteoclasts and replaced by bone-building cells called osteoblasts - a process called bone turnover,' explains Robert Moots, Professor of Rheumatology at Aintree University Hospital in Liverpool .
Children's bone growth is rapid - the skeleton takes just two years to renew
In adults, this can take ten years.
Until our mid-20s, bone density is still increasing.
But at 35 bone loss begins as part of the natural ageing process.
TEETH - Start ageing at 40.
As we age, we produce less saliva, which washes away bacteria, so teeth and gums are more vulnerable to decay. Receding gums - when tissue is lost from gums around the teeth - is common in adults over 40.
MUSCLES - Start ageing at 30.
Muscle is constantly being built up and broken down, a process which is well balanced in young adults.
However, by the time we're 30, breakdown is greater than buildup, explains Professor Robert Moots.
Once adults reach 40, they start to lose between 0.5 and 02 per cent of their muscle each year.
Regular exercise can help prevent this.
HEARING - Starts ageing mid-50s.
More than half of people over 60 lose hearing because of their age, according to the Royal National Institute for the Deaf.
SKIN - Starts ageing mid-20s.
The skin starts to age naturally in your mid-20s.
TASTE AND SMELL - Start ageing at 60.
We start out in life with about 10,000 taste buds scattered on the tongue.
This number can halve later in life.
After we turn 60, taste and smell gradually decline, partly as a result of the normal ageing process.
FERTILITY - Starts ageing at 35.
Female fertility begins to decline after 35, as the number and quality of eggs in the ovaries start to fall.
The lining of the womb may become thinner, making it less likely for a fertilised egg to take, and also creating an environment hostile to sperm.
HAIR - Starts ageing at 30.
Male hair loss usually begins in the 30s. Hair is made in tiny pouches just under the skin's surface, known as follices. A hair normally grows from each follicle for about three years, is then shed, and a new hair grows.
Most people will have some grey hair by the age of 35.
When we are young, our hair is coloured by the pigments produced by cells in the hair follicle known as melanocytes.