All that has been stated on this site applies to the Ukulele too.
There are now graded exams offered by the London College of Music and Rockschool for the Uke.
You don't have to follow a prescribed curriculum.
Learn your favourite tunes. Play for fun. No previous musical knowledge is necessary.
You may be pleased to know that the strings on the Ukulele are tuned such that they produce the same sound as the top four strings on a guitar at the fifth fret so all the chord shapes you learn are immediately transferable to the guitar and vici versa.
Another advantage is that when you burn your instrument at the end of a set or ram it through the front of your amp the Ukulele is much cheaper to replace than a guitar.
The Registry of Guitar Tutors and Rockschool Graded Exam systems are now available.
You'll learn about all the elements necessary to produce a musical performance, rhythm, melody, harmony etc.
Fantastically useful for recording how your tunes go and spontaneously joining in on new ones.
Don't be confined by established repetoire write your own charts.
The ability to follow and write a chord chart greatly aids your understanding of the tunes you're playing, helping you to rehearse and arrange a set and enabling you to join other musicians or acts at short notice.
Learn your favourite tunes. Play for fun.
Don't feel abashed about lacking any previous experience. It's not neccessary. I've taken many adult total beginners up to public performance level.
Peter Sellers was a big fan of George and there's a youtube vid of him giving an excellent rendition of 'When I'm cleaning windows' on the Michael Parkinson show.