Don't rush and overdo it. You wouldn't suddenly decide to run 10K if you hadn't done any running for the last 20years, and it would hurt like hell if you did and you would injure yourself. Fingers are the same as legs, just smaller and they have to move faster.
Hard to do these days, but a real bass teacher is the best thing for starting.The online resources are good if you can sort the wheat from the chaff. Check out StudyBass.com (free) for a really solid foundation including technique, theory, avoiding injury and all sorts. A good complement to learning tunes you like. Scotts Bass Lessons has a good video on warm up somewhere as well. His style is marmite, but I like it and evntually coughed up the £100/year for the paid for stuff.
Just to encourage you: I started 2 and a bit years ago aged 51. I still consider I am a hopeless beginner, and I don't practice anywhere near enough. However I can hack my way through a worship song and not embarrass myself of the band, I can make up basslines that aren't just roots and fifths, and am thoroughly enjoying myself. Most students over estimate what they can learn in a week or two, but underestimate where they could be in a year.
Happy days!