I personally started out on guitar about 2 years ahead of me picking up the bass, which quickly after became my preferred instrument of choice.
I found the transition quite easy in fact.
Although it is not the same instrument, a lot of the techniques, chords and scales can be directly transferred to your bass play with some minor modifications.
I feel probably the biggest difference between the two instruments, beside the obvious octave down of a bass is actually their general role in a band context as instruments.
Personally when I started on bass, after having played guitar for about 2 years, I found that I liked both the sound, feel and role in music of the bass much better and that it somehow were more in line with my personality, it felt like coming home in a way, so bass quickly took over as my main instrument from the guitar.
I felt both more free, secure and comfortable playing bass than I had ever been playing guitar.
It really gave me a huge advantage to have played guitar before though, as I was fairly familiar with the fret board already and that most of what I'd learned on guitar, as I stated earlier in this post, could relatively easily be adapted to suit and serve my bass playing.
Later I found that playing both instruments have improved my skills on both, and I still play guitar on the sideline from time to time.
