Are you talking about babysitting? It would depend on the maturity level of anyone regardless of gender. My nephews who were 10 or more years older than their younger siblings often watched after them. The key to that is you must make it clear they cannot have any friends over. (When teen boys get together sometimes it can be a competition to see who can do the most reckless things.)
I have two15 year old boys who babysit for me, always together.They do a great job and my kids love them. I know their mothers also. The biggest problem I've had was when they fed my goldfish too much and they died.