You can not CCW until you are 21.
Act 235 only allows you to carry a weapon while going directly to or from work and while working. You can not carry for any other reason.
You can be Act 120 certified at the age of 18, however you still can not legally buy a handgun until you are 21.
You can be 18 years of age and "own" a handgun because it was either gifted to you, or passed on to you.
All handgun sales must go through a FFL.
§6111. Sale or transfer of firearms.
(c) Duty of other persons.—Any person who is not a licensed importer, manufacturer or dealer and who desires to sell or transfer a firearm to another unlicensed person shall do so only upon the place of business of a licensed importer, manufacturer, dealer or county sheriff’s office, the latter of whom shall follow the procedure set forth in this section as if he were the seller of the firearm. The provisions of this section shall not apply to transfers between spouses or to transfers between a parent and child or to transfers between grandparent and grandchild.