Prince William will celebrate his coming of age with a birthday party to mark the occasion.
Prince William has a Yamaha 600 trials bike
Here are some of the extracts from his frank and revealing interview, when he reflects on his life at 21.
On his character:
"I'm not an over-dominant person. I don't go around and expect everyone to listen to me the whole time.
"But I like to be in control of my life because I have so many people around me, I can get pulled in one direction and then the other ... I do take in whatever people say to me and around me, and then I'll make my own decision."
On his father Prince Charles:
"He's been given quite a hard time recently and I just wish that people would give him a break. He's very happy and protective towards Harry and me as well."
On his mother Princess Diana:
"I was influenced a lot by my visits to hostels with my mother when I was younger. I learned a lot from it, more so now that I did at the time.
"My mother used her position very well to help other people, as does my father, and I hope to do the same."
On the countryside:
"At the moment there are quite a few challenges facing the countryside.
"To me, one of the worrying things is the lack of affordable housing for the younger generation.
"If younger people leave, there's no future for the countryside. All the inherited skills you get passed down from farmers, for example, will be lost.
On his gap year:
"Working as a farm hand during my gap year was very, very hard. It was the toughness of it.
"Admittedly, I was exhausted after only a week as a dairy farm hand, and the guy I was working with did it every day of his life.
"There were so many genuine people. They didn't care who I was and made me do the jobs I should be doing, like mucking out and driving tractors in the fields.
"They made me see what actually goes on and they trusted me as well."
On his brother Prince Harry:
"I have a very good relationship with my brother, we've grown up together and we have to go through a lot of things together.
"We've grown up around the same things and the same people, and we'll always have that common bond.
"We ring each other quite a lot. He usually rings me up to tell me some incredibly amusing story and the things he gets up to. He is a very nice guy and he's very caring."
"Riding a motorbike can be dangerous but so can lots of things really.
"Admittedly, there are more risks involved in riding a motorbike than there are with other things ... you've just got to be aware of what you're doing.
"My father is concerned about the fact that I'm into motorbikes but he doesn't want to keep me all wrapped up in cotton wool."
On his African theme party:
"I thought it would be quite fun to see the family out of black tie and get everyone to dress up. It just gives a bit of character.
"My grandmother (the Queen) may be slightly apprehensive as to what she's going to wear, and what's going to happen, but she's very much looking forward to it ... I don't know what she is going to wear."
On his birthday present:
"There's nothing specifically I would like - I'll just have to wait and see what's given to me.
"I've dropped many hints to my father about pretty much everything.
"I think I've gone round in circles about what I want and he's given up on me.
"He'll do the paternal thing and decide what he thinks is best - I'm sure he'll give me something lovely."