So ive got quite a young grandma, in her 50's. I'm almost 18. Ive been offered a job at the place she works where the boss said i could only work there if i saw myself having a future there.
I was a bit weary about commiting to that as i am still unsure as to what it is i want to do with my life. So my contract was sent out to me and is still sitting there waiting for me to sign. (They are waiting for me to finish working my notice of my current job)

I had also applied for another job elsewhere a few weeks ago that i really really wanted. After not hearing anything for a while, i thought i wasn't chosen as a candidate so i just forgot about it.
Well yesterday, somebody rang me about that job! They wanted to know if i was still interested and how soon could i start?

My dillema is this.. Can i turn down the job at where my nana works even though i have an unsigned contract? I'm worried it will ruin our relationship as she is very excited for me to start there and says that they're really short staffed and need me ASAP. I don't see myself having a future there. Is it ethiclly wrong to turn it down?? or Should i just forget about this other job?

If you talk to your grandmother about what you want to do I'm sure she'll understand. Wouldn't she rather you were doing what you wanted to do and was happy instead of doing what you think she wants you to do and be unhappy?
If you haven't signed a contract you don't have to work there, no-one can make you.
If I were you I'd go to this other job interview and see what happens. Keep both options open but at the end of the day if you really don't want to work where your grandmother works then don't.
Don't do things to make other people happy, I did and it made me miserable and when I spoke to my family they were upset but understanding. I needed to do what I wanted to make me happy.