if they're not shopped you in good shape bro, i know most will say start when your 21 but it sounds like your set on cycling so do it properly. try test e or c 500mg each week split into 2 doses( most inject 250mg monday and 250mg thurseday) and run this cycle for 12 weeks. for post cycle therapy (pct) use clomid 50mg/50mg/50mg/50mg, start post cycle therapy (pct) 2 weeks after last injection. also i would recomend that you have an Aromatase inhibitor (AI) on hand such as lectro. i would also suggest the use of HCG, this will help stop your balls from shrinking, try 250iu's twice a week starting at week 5 and i personally would run it till you start post cycle therapy (pct). so the layout will look like
week 1-12 test e/c 500mg EW
week 5-14 HCG 500iu's EW
post cycle therapy (pct) 15-19 clomid 50mg ED