Is it normal for an 18 yrs old to still have most the of his baby teeth?

Most, No. It is not normal to have mostly baby teeth at that age, but it is very common for them to have some baby teeth. You need to see a dentist to determine which ones are baby teeth and which ones may still have permanant teeth to replace them. Most baby teeth are lost before age 14.
Can be. Some people have retained "baby" teeth well into adulthood due to the fact that their permanent teeth did not form. The retained teeth can last for many years, however, often they eventually lose their roots (what holds them in place) and will need to be replaced. Have a dental exam/xray to determine whether or not the permanent teeth are missing.