Studies of hydraulic architecture in tall trees indicate that increasing hydraulic resistance with increasing tree size can be mitigated by basipetal widening of xylem conduits from treetop to stem base. The pattern of conduit widening is described by the exponentiation function, which predicts infinite widening of mean hydraulic conduit diameter (Dh). Empirical data, however, suggest the limitation of vessel widening in very tall trees, such as Eucalyptus and Sequoia, and observed Dh at the stem base is narrower than expected by the exponentiation function. Also, the effects of age/size, which can co-vary with height, has not been tested rigorously. Here, to investigate effects of tree age on basipetal widening of xylem conduits and widening limitation, we compared axial variation of xylem structure of mature (ca. 50yrs) and old (ca. 150 and 250yrs) Cinnamomum camphora trees. We fitted saturating equations defining a maximum conduit diameter (Dmax) to the relationship between Dh and stem length and compared potential hydraulic conductivity (Kp). The saturating models fitted better than conventional exponential model. We inferred that Dmax is limited by the hydraulic-mechanical tradeoff in taller trees.