Surfing Waves

I'm a 15 year old girl and I really want to get good at surfing. I have some experience but I go long periods of time without surfing. I can normally stand up when catching a wave but I usually fall off after 8-10 seconds. This summer I have almost 2 whole months where I would be able to surf 4-6 times a week. Would it be possible to learn to short board successfully in this amount of time? (I'm 5'11" and 135lbs and I have a 8' board and am planning on getting a short/funboard) And what size board would you recommend?

Roxxyyyy, for you to rock I would suggest you stick with your longer board for those couple of months.
Why because you will catch more waves, get your skills improving and be able to stay on the board longer, you will be likely to learn how to go across a wave and set up basic turns and linking them.
You will be able to go short in the end but get all your skills together first, short now will mean a lot harder time in all aspects of your surfing.
You could do it 15 is very adaptable. But think about my advice.

The only thing that will improve by going from a 8 footer to a Shortboard is your get off time will go from 8-10 seconds to less than 1-2 seconds ( or none at all, since you won't be able to catch the wave and stand up )
Getting on a Shortboard shouldn't be your goal. Riding the wave should be. Standing up for a few seconds is just a delayed fall, where you're just trying to stay on. Until you can control / decide where the board should go, you shouldn't go smaller than what you're on currently.

If you start to feel confident on your longboard, then there's nothing wrong with renting a shortboard and giving it a try. You'll likely go back to longboarding, but the mystery of shortboarding will be gone. In my opinion, it's a good idea to get some idea of the difference between a shortboard and a longboard. That might lead you to understand how certain waves are suited to a shortboard as well as start to undersand the wave riding possibilities of a longboard.

Roxyyy, you are very cool. I wish I'd learn to surf when young. Keep the stoke!
an Old Guy named billie

One of the problems we hear on this forum is beginners wanting to ride a shortboard and after purchasing one find they can't catch a wave with it. If you are falling off your 8 foot board for unknown reasons after a few seconds that sounds like more fun than not being able to catch or ride a wave at all. If you could rent one that might help you decide.

You begin to go to surfing at 15. So cool.