A 6-Month cardiovascular fitness routine for 14-year-old?

[blahblahboy]

I'm 14-years-old and 1.6 metres (5'3") and I intend to trek Mt. Kilimanjaro in July 2011.

Can anyone recommend a good 6 month routine I can follow to train my cardiovascular fitness?
Oh, and I weigh 49kg, 109lbs.