If i am now 18 years old .my breast aches when i touch it .is this normal?

Depends on timing: Many women experience breast fullness/tenderness associated with menstrual cycles (your period). If you have periodic tenderness that is then better for weeks at a time, this might be the cause. I assume you are neither pregnant nor breastfeeding. Those could also cause this. If you have persistent tenderness in one area and have not been injured, it may be a good idea to have it checked at md.