An age-progressive platelet differentiation path from hematopoietic stem cells causes exacerbated thrombosis. As people age, platelets generated through a shortcut differentiation pathway that bypasses the canonical progenitor cascade to directly produce megakaryocyte progenitors (MkPs) from hematopoietic stem cells (HSCs) become more prone to thrombosis. This pathway leads to thrombocytosis and platelet hyper-reactivity, contributing to age-related thrombosis. The study reveals that aging leads to two distinct platelet specification paths from HSCs: a shortcut path and a canonical path. The shortcut path is characterized by highly expansive MkPs that produce an additional platelet population in old mice. These age-enriched platelets are functionally hyper-reactive compared to canonical platelets. The findings suggest that stem cell-based aging is a mechanism for platelet dysregulation and age-induced thrombosis. The study used the FlkSwitch mouse model to track hematopoietic differentiation pathways and demonstrated that the shortcut pathway leads to increased platelet production and hyper-reactivity. Age-enriched MkPs are transcriptionally distinct and have enhanced functional capacity, contributing to thrombosis. The study also shows that age-enriched MkPs rapidly restore acute thrombocytopenia and participate in exacerbated clot formation upon vascular injury. The hyper-reactivity of old platelets is evident in their increased aggregation with leukocytes and their enhanced response to thrombin. The findings highlight the role of stem cell aging in platelet dysregulation and suggest that targeting HSCs and MkPs could be a therapeutic approach for controlling thrombosis in the elderly. The study has limitations, including the difficulty of reproducing findings in wild-type strains and the need for a more stringent definition of MkPs. The results provide new insights into the mechanisms of age-related thrombosis and the potential for therapeutic interventions.An age-progressive platelet differentiation path from hematopoietic stem cells causes exacerbated thrombosis. As people age, platelets generated through a shortcut differentiation pathway that bypasses the canonical progenitor cascade to directly produce megakaryocyte progenitors (MkPs) from hematopoietic stem cells (HSCs) become more prone to thrombosis. This pathway leads to thrombocytosis and platelet hyper-reactivity, contributing to age-related thrombosis. The study reveals that aging leads to two distinct platelet specification paths from HSCs: a shortcut path and a canonical path. The shortcut path is characterized by highly expansive MkPs that produce an additional platelet population in old mice. These age-enriched platelets are functionally hyper-reactive compared to canonical platelets. The findings suggest that stem cell-based aging is a mechanism for platelet dysregulation and age-induced thrombosis. The study used the FlkSwitch mouse model to track hematopoietic differentiation pathways and demonstrated that the shortcut pathway leads to increased platelet production and hyper-reactivity. Age-enriched MkPs are transcriptionally distinct and have enhanced functional capacity, contributing to thrombosis. The study also shows that age-enriched MkPs rapidly restore acute thrombocytopenia and participate in exacerbated clot formation upon vascular injury. The hyper-reactivity of old platelets is evident in their increased aggregation with leukocytes and their enhanced response to thrombin. The findings highlight the role of stem cell aging in platelet dysregulation and suggest that targeting HSCs and MkPs could be a therapeutic approach for controlling thrombosis in the elderly. The study has limitations, including the difficulty of reproducing findings in wild-type strains and the need for a more stringent definition of MkPs. The results provide new insights into the mechanisms of age-related thrombosis and the potential for therapeutic interventions.