Is it realistic for a 17 year old to begin to learn how to play the piano?

I have a keyboard and have taught myself a few tunes on it such as Delta Goodrem- Fragile and Death Cab for Cutie- What Sarah Said
however i would love to learn to play piano properly and wondered if it was a sensible and realistic goal for me to achieve?
(With a piano teacher of course)

Is it viable to learn violin (fiddle) well enough to play English Folk music without getting regular lessons?

I already been playing concertina for nearly 2 years and melodeon (one row and 2 row) for just over a year both of which I’ve learnt from books, dvd’s, youtube and the occasional workshop.
I’ve like to learn the violin (fiddle) as the more I get into english folk music the more I realize some tunes may be easier on violin (fiddle) plus I like the thought of not having to get a new instrument for every different key I want to play. I do know 2 people who play violin so i could get them to help spot any bad habits.
So any suggestions on good books/dvd’s to start with.
I’m quite happy to spend months just playing scales its the only way the concertina finally ‘clicked’ so I could play in more than the home keys.
Any forums or websites with resources you can recommend.