At your age, another thing to consider is the ability to grow into your stick. Those new sticks that cost upwards of 300$ now will put a dent into your pocket.
I’m not sure how your junior stick is long enough for you, but the intermediate isn’t. Like another poster said, there are extensions you can add as well.
No one is able to tell you the right flex or length for your hockey stick, but there are some suggestions I can give to you.
1. When it comes to flex, make sure you are able to utilize it. If you aren’t, don’t be afraid to use a whippier stick.
2. I’ve heard the preference of defensemen to have a longer stick, as it’s easier for gap control, stickwork, etc, again- all preference.
3. Now this is something that goes beyond flex and length. Your kick point, do you take big slappers from the point? You’re going to want a mid kick stick. If you take quick snappers, low kick stick.
My suggestion? Find an intermediate stick that is long enough for you. It might be too stiff at first but atleast you’ll be able to grow into it. And if I remember correctly you shouldn’t have an issue with an intermediate stick being too short if your junior stick works. I know grown adults that use 67 intermediate sticks.