I'm a 27-year-old guy.

My problem is that I have quite large buttocks. Please, apart from surgery, what can I do to reduce their size?

Thanks.

For one thing cut out all junk food, processed food and transfats.
Use good oils.

See if this site is helpful
http://www.pompahealthsolutions.com/index.php?option=com_content&task=view&id=25&Itemid=58

Walking and or jogging is very good exercise.
It is a lifestyle change. Not only change in diet, but change in lifestyle by regular exercise.

Thank you to both of you.