When you should start training depends on 3 main factors: 1) The trip’s itinerary 2) Your current activity level 3) The amount of time you have in your schedule to train. For most multi-day hikes with a lot of elevation change and challenging terrain - Kilimanjaro, Peru, Patagonia, Cotopaxi - reasonably active women would be wise to allow at least 3 months to get ready.