The age of the seedlings in the transplant, as well as the use of biostimulants in their production, are factors that can influence the good quality of the seedlings, which is fundamental for the good development of the plant, and can affect the yield of the tomato crop. The objective of this study was to evaluate plant development and fruit yield according to the age of tomato seedlings, during transplantation, whether or not treated with the Stimulate® biostimulant. The hybrid H9553 was used, and the experiment was conducted in a randomized block design, with four replications, and ten plants were evaluated, per plot. The factorial scheme 2 x 6 was adopted, where 2 corresponds to the use or not of Stimulate®, and 6 corresponds to the age of the seedlings, in the transplant. Before transplantation, the height of the seedling, length of the root, stem diameter, number of leaves, fresh and dry mass of the aerial part and the root were evaluated at 20, 30, 40, 50, 60 and 70 days after sowing. At 78 days after transplantation, the length of the main stem, stem diameter, number of fruits per plant, total fruit mass per plant and average fruit mass were evaluated. Seedlings with seventy days show superior results for the morphological characteristics, however, this does not interfere in the yield of the culture. The use of Stimulate®, alone or in interaction with the age of the seedlings, does not influence plant growth or fruit yield.