"Adults only? Why?"
I simply find people over 16 more enjoyable to teach! They want to learn and are enthusiastic, dedicated and conscientious about practicing. For piano I use a piano course specially written for adult learners. This delivers a comprehensive education in music theory as well as practical skills.
"Do I need an instrument?"
For Piano you do need something to practice on - even if it's only a digital piano - but best of all is a real acoustic piano. I recommend Shackleford Pianos for a reconditioned 2nd hand upright with a three year warranty at a sensible price. Keyboards are not really suitable to learn to play the piano on - they don't have enough keys, they don't have weighted keys, they don't have pedals.
For Flute I recommend a Yamaha 211 for beginners - this is easy to play, has a good tone and has a good resale value should you want to upgrade one day. You can often get a reconditioned 2nd hand one from JustFlutes.com
"I don't know anything about music - is that a problem?"
Absolute beginners are very welcome. I assume no musical knowledge at all.
"Would I need to practice?"
About 20 minutes a day to begin with would make for good initial progress. It shouldn't be a chore though.
"Do I have to learn to read music?"
That's how I teach, but just a little at a time. It's worth it in the long run to become confident at reading music. You can then play things you don't already know.
"Can I take exams?"
Adults are welcome to take music exams by all the main exam boards. Exams are available in Piano, Flute, Jazz Piano, Jazz Flute, Music Theory (written exams) and Composition (postal exams!). See my Exams page for the latest candidates and results. Exams are a good way to measure progress but are not essential. Playing for pleasure is what it's all about really.