My own experience, growing out my hair long before I even dared admit I was trans to myself, has been that long hair is no problem at all. You go through a slight awkward stage, but if you wanna present as male and care about how people see "male you" (which I didn't), some hair gel should do the trick until the hair grows long enough to officially go from "is that short, or is it long?" "to short half-long" (which is a subcategory of "long"). Grow it down to below the jawline, and that's about when you hit the magic spot - and before that, it can be styled as short hair.
Bottom line: IME, there's pretty much a point where your hair just flips over from short to long overnight - or, over a week or so. There should be little issue.
(This spoken by someone who was conscripted and spent a short while in the army with hair down to the middle of my shoulder blades.)