Have a look at JSP 440, Part 6, Section 4. If you are DV cleared then further restrictions may be in place and your age too is also taken into consideration. One of the things you may need to ask yourself is are you travelling on business or pleasure? If with work, then think about what you are taking with you and the threat in the location you are visiting/working. The F&CO website is aslo useful for tips, help and advice. I do have some experience of working within some of the restrictions and sending folks off to far off locs so if you are well and truly stuck please let me know.