Most treks walk for an average of 4-6 hours per day, broken by a lunch stop. On most trekking days you can expect to gain a maximum of 700m, this will drop to 500m above an altitude of 3000m, however on some of the harder treks over 1000m of ascent can be covered on some days. Usually trekking will begin in the early morning after a breakfast and will end early to mid afternoon, this pattern is adopted to avoid the hottest part of the day. On most treks there will be support to carry your equipment and most of your baggage, this can range from Sherpa's and other local peoples to Yaks, donkeys and even camels. You will usually be expected to carry a small rucksack with water and other personal items for the day.
Accommodation is generally in tents or local lodges which are of a basic nature.
It is advisable to take some warm clothing for the evenings as temperatures can drop quite low once the sun has set. It is also important to remember that the pace you walk at home and in the valleys will be significantly faster the your pace at altitude. The best training before you go is of course walking, but cycling, swimming and other activities are good to boost your general level of fitness. If trekking at high altitude it is worth arriving at the start of your trek a few days before it begins to enable your body to acclimatize to the lower amount of oxygen in the air. Finally, age is no barrier to trekking, as long as you are reasonably fit a trekking holiday is for you.