Both my parents have now split (ages ago) and i was bought a tandem jump as a Xmas present last year off my father (did the jump June 3rd, and loved it). My mum really hated the idea of me jumping and if it was up to her i wouldn't of done it (being 18 it was my choice any how).
When i came back that day, still buzzing, i told my mum that i will be doing the AFF course next year. My mother told me that she does not want me todo it but, as i'm an adult, its my choice.
The fact is your only 17 and until you can jump without your mums permission unless she is happy (or as happy as she could be) with you jumping then you should respect your mums choice. Fell the Fear, do it anyway !