It's never to old to Trans Plant.
First of all is what I do is, get your Medium in your 5 gallon or bigger pot, take the container that your using now and place it in the new pot towards the top of new pot fill new pot so that the old cup is in the new pot and leave that space in the new soil, pack the new soil down lightly and pull that cup out so there's a space in the new pot that will fit that new plant into, Roll the Solo cup in between your hands to break it loose from solo cup, Easy. next put your plant between your middle and ring finger tip solo cup upside down and it should fall out and sit in the palm of your hand now be easy and flip it into that space you provided in the new soil it should fit perfectly.
If your easy you shouldn't loose any Medium off the new plant if you do just be really easy and put it into pot like stated above. Water Around new in the new soil and presto there you go. Remember it's never to late to transplant. Good luck.