Anyone who can ride a bike can complete an end to end cycle. However, if you are not fit enough and do not eat the right sort of things then it might take you a long time and it might not be very enjoyable.
Most people will need to do some training before cycling Lands End to John O’Groats. There are books and books written about cycle training but I have tried to summarise the basics of what you might need on the training page. It includes a rudimentary 10 week end to end training plan that you can adapt to the duration of ride you intend and your current fitness level.
Equally important to your success on your end to end cycle is getting the right sort of nutrition. Again there are countless books available that can help you. I have distilled out the main things you should know about nutrition for your end to end with special attention paid to hydration during your ride. It is important to get the nutrition right early on. You need to eat and drink correctly whilst you are training to get the best out of it.