In its diverse forms, authentic writing carries the potential to connect literacy practice to an author's 'real world'. While contemporary approaches to authentic writing instruction--advocating writer-centred, intertextual and culturally relevant productions--are most often explored in formal learning contexts like classrooms, this paper seeks to amplify the mentorship strategies employed within an informal youth centre learning space in Montreal, Canada. The following research questions have guided this work: (1) How do adult mentors leverage authentic writing principles to support adolescents' participation within two writing-based programmes developed in a youth centre context? (2) How do the interests, perspectives and backgrounds of adult mentors shape the mentorship strategies they choose to employ? Data collected and analysed through participant-focused ethnographic approaches assist the author in revealing how adult writing mentors draw from their own cultural, linguistic and embodied experiences to foster interest-driven, culturally sustaining and community-based writing opportunities for adolescents. The four key mentorship themes emerging through this research--centring the essential role of writing "journeys," "identities" and "communities" while acknowledging several "barriers" to authentic writing--advocate drawing from the rich literacy practices thriving within informal contexts to inform contemporary writing curricula.