Big Brothers/Big Sisters is a brilliant organization, and if you feel the inclination to serve your community in this way, go in and talk to someone.
It is a big decision (no pun intended) and their vetting process is impeccable. They are used to talking to people about how things work, the level of commitment involved, and ensuring people are fully informed and fully committed.
It is, after all, a child's life we are talking about, here.
All that said, my Dad is a Big Brother, and he was President of Big Brothers of Greater Los Angeles. My sister is a Big Sister. And I opted out of becoming a Big Brother because my life was in chaos at the time.
Go in. Talk to them. Even if you are just thinking about it, they can help you get your head around the "unknown unknowns" that you haven't even considered.
It is a big commitment, but also hugely rewarding.