Your 20s is a great time to be a founder. You have fewer responsibilities so can get by with less income and more easily up sticks to somewhere else. Your opportunity cost as a junior is low. It's a bad time to get a job as a junior too, so this is a good way to get job experience if nobody will hire you. You probably won't succeed (because most startups fail) but you'll learn a lot and probably have a lot of fun.