A new aggregation model by a Molecular Dynamics approach at constant temperature was compared with experimental results on a zirconia precursor gelling process. The evolution of the distribution of the experimental scattered intensities (small angle X-ray scattering curves), during gelling, was compared with the results of our Molecular Dynamics method, via the computation of structure factors of the numerical structure for different times: a very good agreement was found. Our numerical model allows one to understand the evolution as a function of time of the size and quantity of matter corresponding to the upper limit of the fractal domain.