Well, the bowed string instruments are certainly among the easiest to get technically wrong. I tried to learn cello for more than one year before taking lessons (at the age of 16, incidentally), and not much came of it. Even incredible musical polymath Rob Scallon's cello stuff, while definitely impressive in a way, is really nothing that could be called good cello playing in a classical sense. So if you eventually want to play classical music, you very likely won't get around some real lessons.
But I agree with Tim: bad habits aren't impossible to get rid of; some of them may hinder you a bit longer than if you'd learned it properly straight away, but among the bad habits you'll learn also a couple of good skills automatically, and most importantly get a rough feeling for the instrument, so I'm pretty sure it's better to start badly than to not start at all before learning properly.
In particular, I do think you can become a decent Bluegrass bassist autodidactically. There certainly are quite a lot good self-taught Rockabilly double bassists around.