Alpha (α) particles and low-energy beta (β) particles present minimal risk for external exposure. While these particles can induce leukemia and bone cancer due to internal exposure, they can also be beneficial for targeted radiation therapies. In this paper, a trabecular bone model is presented to investigate the radiation dose from bone- and marrow-seeking α and β emitters to different critical compartments (targets) of trabecular bone for different age groups. Two main issues are addressed with Monte Carlo simulations. The first is the absorption fractions (AFs) from bone and marrow to critical targets within the bone for different age groups. The other issue is the application of (223)Ra for the radiotherapy treatment of bone metastases. Both a static model and a simulated bone remodeling process are established for trabecular bone. The results show significantly lower AFs from radionuclide sources in the bone volume to the peripheral marrow and the haematopoietic marrow for adults than for newborns and children. The AFs from sources on the bone surface and in the bone marrow to peripheral marrow and haematopoietic marrow also varies for adults and children depending on the energy of the particles. Regarding the use of (223)Ra as a radionuclide for the radiotherapy of bone metastases, the simulations show a significantly higher dose from (223)Ra and its progeny in forming bone to the target compartment of bone metastases than that from two other more commonly used β-emitting radiopharmaceuticals, (153)Sm and (89)Sr. There is also a slightly lower dose from (223)Ra in forming bone to haematopoietic marrow than that from (153)Sm and (89)Sr. These results indicate a higher therapy efficiency and lower marrow toxicity from (223)Ra and its progeny. In conclusion, age-related changes in bone dimension and cellularity seem to significantly affect the internal dose from α and β emitters in the bone and marrow to critical targets, and (223)Ra may be a more efficient radiopharmaceutical for the treatment of bone metastases than (153)Sm and (89)Sr, if the diffusion of (219)Rn to the bone marrow is insignificant.