Hi there,
I started off on guitar when I was 10 years old. What happens quite often at high school is all the guitarists eventually find each other and decide to form various bands. Suddenly everyone notices, wow, we have seven guitarists, anyone want to get a bass for their next Xmas and someone a set of drums and maybe a keyboard player....hmmm... that was how I ended up playing bass.
I then had bass for my main instrument for years when I started playing in my dad's jazz band.
I will say one thing though. Bass becomes a lot easier if you have an understanding of at least basic chord structures and scales. To go straight into playing bass with no previous musical experience is very hard.
Later on, I found I was one of those bassists who found they could not play good bass and sing at the same time. So, I changed back to guitar and started writing songs and singing. That's what I've done ever since and I like it a lot.
Cheers, Gordon.