This book explores the interplay between arterial hypertension (HTN), subclinical hypothyroidism (SCH), and ageing processes, emphasizing shared mechanisms such as low-grade inflammation and oxidative stress. It highlights the limitations of calendar age as an ageing indicator and advocates for biological age (BA) as a more accurate measure influenced by lifestyle, health conditions, and interventions. Given the absence of widely accessible tools for assessing BA, the book outlines a novel methodology for evaluating premature ageing in patients with HTN and SCH.The study, based on original research data involving 150 participants divided into three groups (HTN with SCH, isolated HTN, and healthy controls), examines the role of cardiometabolic factors, oxidative stress markers, and inflammation in ageing trajectories. Drawing on these findings, it introduces a risk stratification algorithm to identify patients at high risk of premature ageing. Practical recommendations for screening and therapeutic strategies are presented, emphasizing personalized management approaches to mitigate cardiovascular risks and regulate ageing rates.