Iconically - if you’re studying, don’t get too wrapped up in PE. Sure, keep in on the side as a hobby type thing, but if you find yourself putting off assignments to stroke yourself off, just play it safe and put it on hold.
You can always resume PE later down the track when you have time, but if you fuck up in school, it can be hard to get a second chance. (I should be taking my own advice ;) )
I would guess that if you are around about an average gainer that you would probably get about an inch or so in length and maybe 1/2-1” in girth in 18 months time, following a proper routine. But that is of course assuming all goes well, that you don’t injure yourself, and assuming you are not a hard gainer or anything. So don’t take that as gospel, just an optimistic average. Good luck!