Background: Given varied forms of stressors in the backdrop of the COVID 19 pandemic, adolescents are particularly vulnerable to specific mental health challenges. It pertinent to explore how adolescents differ from adults regarding the comprehensive mental health facets amid the 'new normal, i.e., the duration between the first and second wave of COVID-19 in a developing country like India. The present study aimed to compare the comprehensive mental health facets of adolescents with the adults. Also, it aimed to explore the association of mental health facets with age, perceived stress, coping and impact of pandemic. Methods: The study followed a cross-sectional design with 1,027 participants [456 adolescents; 347 young and 224 middle age-adults] recruited from schools and colleges. The Comprehensive DSM-5 Self-Rated Level 1 Cross-Cutting Symptom Measure, Perceived Stress Scale and Brief COPE Scale were used for assessment. The difference between groups was analyzed using the Chi-Square Test of Independence and correlational analysis was done using Spearman Rank Correlation. Multiple regression analyses were performed for the mental health facets along with bootstrapping method. Results: 33.77% of adolescents, 25.65% of young adults, and 17.41% of middle-aged adults reported that their symptoms started during the pandemic. Compared to adults, the adolescents reported higher depression, anxiety, suicidal ideations, anger, and somatic complaints. Significantly higher adolescent females (39.9%) were found to have sleep disturbances compared to their male counterparts (25.5%). Therefore, it can be observed Adolescents are more clinically vulnerable in most domains. The correlational analysis showed that most mental health domains, except substance use showed moderate-to-low correlations with ‘Impact of COVID’. Perceived stress, impact of COVID, self-distraction, self-blaming were significant independent positive predictors for all the mental health domains except substance use. ‘Age’ was negatively associated with depression anxiety, repetitive thoughts, personality changes, suicidal ideations and memory, and positively associated with ‘substance use’ at low levels. Maladaptive coping was moderately positively correlated with all the mental health domains. Conclusion: It can be observed Adolescents are more clinically vulnerable in most domains. This study provides a comprehensive analysis for assessment and clinical decision-making to combat the mental health problems arising and exacerbating due to the COVID-19 pandemic. The findings will help in planning and implementing an appropriate interventional program, and making policy decisions related to the vulnerable group of adolescents.