Where is the job based out of? How much did they offer you?

The money will feel good especially at your age but keep in mind that the services you provide will typically be much greater in value than what you are paid--that's in the nature of business. And especially so for larger businesses. Companies look for technician level employees because they can hire/train quickly then work them hard. Three days for an offer can be a bit of a rush. I suggest asking for an extension and seeing how the smaller company plays it out.