Background: Parent–adolescent communication, peer relationships, autonomy, identity, and future-related thinking are often studied separately, despite their potential relevance to emotional adjustment during the transition to adulthood. Age-specific evidence for late adolescence and Saudi/Gulf settings remains limited. Objective: To critically synthesize evidence on these relational and developmental domains, distinguish association from temporal evidence, and identify a bounded Saudi/Gulf research and clinical agenda. Methods: This targeted narrative review retained a structured PubMed/MEDLINE search audit, final source-level eligibility re-screening, and purposive, citation-tracked source assembly. Three prespecified searches returned 9,443 records before deduplication. The first 20 records in PubMed’s default most-recent ESearch order were retained from each query as a 60-record search audit, not as a relevance-ranked inclusion screen. Twenty-two source records initially informed the synthesis; one out-of-scope source was excluded, leaving 21 original scholarly sources. A separately documented focused age-specific search then added two source-verified records, yielding 23 scholarly sources overall. Findings: Adolescent-rated parent–child communication quality and broader family relationship quality are consistently associated with mental-health outcomes, but much evidence is cross-sectional or based on one informant. Direct 15–19 evidence is narrow: one age-specific prospective synthesis addressed future-related thinking, one 15–19 relationship-profile study was cross-sectional, and one age-18 exposure study measured outcomes at age 21. Mixed-age samples must not be interpreted as age-specific evidence. Saudi and Gulf evidence provides important contextual and service-use information but does not yet provide a direct age-specific test of an integrated parent–peer–autonomy model. Conclusion: The review offers a hypothesis-generating framework and a transparent research agenda. Family-inclusive prevention may be useful when it is acceptable and safe, but the reviewed evidence does not support causal claims, diagnosis from appearance or friendship changes, or a stand-alone family intervention as treatment for mental disorders.