Plantations are primarily located in arid and semi-arid regions, where they significantly enhance regional ecosystem quality and service functions. Yet, recent climate warming has triggered widespread growth decline and tree mortality in these areas. In this study, we developed tree-ring width chronologies for Simon poplar (Populus simonii) across four age classes-young, middle-aged, mature, and overmature-in a typical area of the desert-shelter forests in the Kubuqi Desert of China. The aim was to examine age-dependent differences in growth decline and climate sensitivity across developmental stages. The results revealed distinct temporal variations in tree growth rates around 2010 across all age classes. Simultaneously, climatic sensitivity exhibited significant divergence during this transition period. Prior to 2010, Simon poplar exhibited relatively high radial growth rates and strong climatic sensitivity, with overall warming conditions promoting tree growth similarly across all age classes. After 2010, however, radial growth rates declined markedly, accompanied by a reduction in climate sensitivity. Climate warming induced drought stress exerted an overall inhibitory effect on growth after 2010, with suppression being more pronounced in mature and overmature stands than in young and middle stands. These findings provide empirical evidence for understanding the age-specific responses and possibility of tree mortality to recent intensified drought stress for desert-shelter forest in the Kubuqi Desert and offer scientific guidance for the sustainable management of plantation forest in northern China under changing climatic conditions.