It shouldn’t matter, other than you may still be growing and so some “gains” may just be from late puberty growth. But hey, any growth is good, eh?
As for wanting to grow so much, I think it depends on your ligs somewhat. It seems some guys can just gain a quick inch or more just from ligs, while others of us don’t get that easy growth. Furthermore, 7x7 is a bit absurd, at least on the girth side. If you could even get to 6 x 5, that would put you on the higher end of ‘average’.