People associate ageing with everything running down, getting slower, wearing out. There's the dreaded moment when our eyes first need spectacles. Usually our hearing is next to go. I regularly fear the din that will greet me when I enter a crowded room, and wonder how I'll make sense of individual voices. We can, however, do something to keep our creaking limbs subtle and active. My own health is pretty good for my age: I have the right levels of blood pressure but too high cholesterol, which I'm tackling through diet. But my general fitness, I believe, is due to modest amounts of regular exercise.

In my 40s and 50s I did very little, but, contrary to received opinion, you need more as you get older. Exercise gets oxygen into the body, keeps the circulation going, and simply takes you out of the house.

You can't avoid how you look when you're on television, so I had a painful realisation in my late 50s that I was getting "old woman's stoop". I looked around at those of my own age who still stood tall. As a regular theatre-goer I was quick to notice that Judi Dench and Sheila Hancock had the walk and posture of younger women. Backstage at the National Theatre I saw a noticeboard with information about lessons in the Alexander technique, its tone implying this was no optional extra.

The Alexander technique isn't a treatment or a series of exercises. It's more like a way of learning how your body works and educating it to minimise the tensions that a lifetime's bad habits have built up. Just think how clumsily we bend from our waists to pick up weighty items, putting all sorts of joints at risk. I went along for a couple of courses of 40-minute sessions. I learned about balance, support and coordination. These were quiet, almost contemplative times, when I made minor but significant adjustments to the way I stood, sat and moved. I liked it: it felt restful and right. Then I tried to integrate what I had learned into the daily round. I still do it, but it has become almost automatic. And I notice that whenever I forget the lessons, the tensions return and I feel lumpy and wrong.

Getting old is punishment enough, so I compensate by upping the amounts of body care I lavish on myself. Some 15 years ago I visited a health farm, where among the various treatments, consultations and advice, I had my first encounter with Pilates. I have been doing it regularly twice a week for 14 years now and it is particularly appropriate for ageing limbs and muscles.

Pilates is a series of movements that realign the body through the correct balance of the spine and the core muscles of the body. The exercises are done slowly, on various machines, in coordination with breathing. There's none of the unpleasant stuff that goes with more vigorous exertion: breathlessness, sweat and getting red in the face. Each person is guided into a routine that particularly suits them. After I fell off my bike, Pilates was an important part of my recovery. The bike ride was probably a mistake: an enthusiastic holiday excursion with my grandchildren entered into with no preparatory exercises. I know better now.

Pilates also urges people to push their bodies to the limit of their capacity. Over the years, my bends and stretches are beginning to lose the reach they once had, but I'm certainly more spry than I would be had I done nothing.

Then there's heavy aerobics where you do sweat and get red in the face. I'm not keen on it at all. I hate it, in fact. All that thudding, jumping and pounding away. But I know it should be done. I manage a brief stint on the treadmill every now and then, when under pressure from others. "The heart is a muscle like any other and must be exercised," they say. I make feeble excuses about not jolting my joints, but I know it is self-delusion really.

So I've opted to take more exercise in daily life. Walking - given the lessons of Alexander and Pilates - is a real pleasure. The mind can spool free, noticing, in cities, the varieties of architecture and buildings, and in the country the turn of the seasons and its wildlife. There's no better time to quieten an uneasy spirit, set squabbles in perspective, and even lay the ground plan for any work in progress.

It doesn't all have to be out and about, of course. That move to the bungalow should be delayed as long as possible. Flights of stairs are great for all the muscles even if you get a bit puffed on the way. People swear by gardening to keep them fit, but I suspect it is also full of hazards to backs and muscles. Spring cleaning is great, taken slowly. And I'm thinking of buying an exercise bike.

Taking all this a stage further, I'm beginning to take walking holidays, or at least long weekends. You don't always have to go in groups, you stay overnight at attractive and modest accommodation, and have your luggage taken ahead for you. Distances can vary to suit different degrees of stamina. I don't yet do more than 10 miles a day, but I have invested in some seriously professional walking boots, hiking socks and a walking stick, so I'm signalling my intentions - to myself as much as to others. All these are pleasures that have come to me late in life. And I know my limitations. The maps of the Pennine Way were severe enough to put me off. I made for the gentler Cotswold Way, instead. I know that in the weeks beforehand, I must get into shape. Takes time, takes effort. But then where's the rush? Old age has time enough.