I started running with a friend of mine and we typically run 4-5x a week at minimum and usually it's with a few other friends. It was the best decision I've ever made and am so glad I started running with him.
DOOOO ITTTTT!!!!!!!!!!!!!!!!!
Who cares if you're fast or slow, you will be running and that's all that matters!
You can 100% handle this. I know plenty of people who have done a 1/2 with their longest run in training only being 9 miles. I don't really recommend it, but certainly do-able. By the end of training I'll bet with your base you'll be ready to run a great first half marathon. GL!
You are definitely ready to train for a half marathon, with where you are now.
Whether you are ready for this particular group may require asking a few more questions. How much speed work are they doing? How many mpw? How many runs per week? And how do those answers fit with what you've done to date?
I wound up with a stress fracture training w/ a half marathon group last year for what was supposed to be my first one. I had done a 15k race shortly before starting, so I was right about where you are. The group was running 5 days/week, and I just wasn't ready for that. I finally successfully did my first half this spring, training on my own at a level that I was more prepared for.