Mostly mentoring is understood in the sense of a more experienced person mentoring a new or junior colleague. But as you progress, colleagues can ‘peer-mentor’ each other either in particular areas (such as teaching observation or project management) or for general support.
However, peer mentoring should still be about progress and development, and be equally supportive of each partner.
Peer mentors should hold each other accountable for their action plans, and help each other to achieve their goals.
Some of the courses offered by PPD (eg Springboard) facilitate peer-mentoring, as well as helping you to network and find suitable mentors. Sometimes these peer groups can span a number of years, as members change, develop, move on, but still continue to support each other through different transitions.