I worked on one top that took 18 months to finish - all hand appliqued and hand quilted. The next top I had finished in a weekend (Irish chain Quilt in a day) but I prefer to hand quilt - so that will take a month or 2 to complete.
I agree with the ladies here - choose projects that appeal to you (the ones that piece easily are my favorites!) and colors you enjoy working with. You need a sense of enjoyment while you quilt - otherwise it just becomes an obligation to someone and another deadline to meet. You have to enjoy the journey - not just the destination!
I'm in my mid 40's and started quilting when I was 26. I had to stop for a decade while the kids took all my spare time. I envy the retired ladies at our guild!
Happy Quilting!