We used a spherically symmetric perturbation model and derived a relation between the average density of galactic halo and its epoch of formation. and hence obtained an estimate for the epoch of formation of our Galaxy, t v . With the age of the Galaxy, t G , represented by the age of its globular clusters, the age of the universe is T G + t v . For flat universe models with Ω λ = 0.0, 0.7 and 0.8, we calculated the compatible range of Hubble's constant. It is shown that if the Hubble constant is as large as 80 km s - 1 Mpc, then we may not be able to solve the problem of the age of the universe by introducing the cosmological constant.