Aging is a critical determinant of regenerative capacity in many organ systems, but it remains unresolved in the lung. This study examines murine lung cell dynamics during age-dependent lung regeneration. Proliferation of lung progenitor cells (EpCAM(neg)/Sca-1(high) lung mesenchymal stromal cells - LMSCs, EpCAM(pos)/Sca-1(low) epithelial progenitor cells, proSP-C(pos) alveolar type II epithelial cells - AECII, and CD31(pos) - endothelial cells) was tracked to day 3 or 7 after pneumonectomy (PNX) or SHAM surgery in 3, 9, and 17 month mice. In 3 month mice, post-PNX LMSC proliferation peaked early (3 days), with 50%-80% more BrdU-positive cells than the other cell types, which peaked later (4-7 days). In older mice (9 and 17 month), abundance and post-PNX proliferation of LMSCs at day 3 were reduced (40%-80%). In both young and old mice, LMSCs were isolated and compared phenotypically with whole lung non-LMSCs. Donor age had no qualitative effect on the phenotype (LMSC vs. non-LMSC), with increased expression of CD90/Thy1, CD105/Eng, CD106/Vcam, CD146/Mcam, and Pdgfrα, and up-regulation of mRNA encoding Fap, Eln, Col1a1, Col3a1, Aldh1a3, Arhgef25, Dner, Fgfr1, and Midkine. However, compared with LMSCs isolated from young mice, LMSCs from older mice exhibited reduced mRNA expression of retinoic acid (Aldh1a3, Rbp4), Fgf/Wnt (Fgfr1, Sfrp1, Wnt2, and Ctnnb1), and elastogenesis (Col1a1, Eln, Fbn1, and Sdc2) pathway genes. Isolated LMSCs from older mice also demonstrated lower colony-forming units (-67%), growth potential (-60% by day 7), ALDH activity (-49%), and telomerase activity (-47%). Therefore, age is associated with declining proliferative potential and regenerative functions of LMSCs in the lung.