for a cycle. At your age, and especially a first time....I would simply use 1 ml E5D. if you get say, some test Enanthate and its 200 or 250 or 300 mg per ml then I'de just go with 1 ml E5D.
You will likely feel like a bazillion bucks. I can tell you I messed with AAS in my early and early/mid 20s and havnt touched it in 8 years, until this year(im 33) and Even at my age I feel the effects differently now than back then. Not just the muscle building effects ofcourse, but the "health" effects. Energy, well being, feeling "good" from it ect.
But as these guys said, make sure your kidneys, liver, heart, blood work(cholesterol, trigycerides ect...) are all good. Get a check-up before cycle, mid cycle(with bloodwork) and post cycle.
For all intents and purposes it should be a great experience for you.