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Abstract: I will argue that if dark matter is produced via processes with subhorizon correlation length in the early universe, then there is a lower bound on the mass of dark matter particles [m > 10^(-19) eV]. For such dark matter, there is both (i) a free streaming suppression and (ii) white-noise enhancement in the dark matter density power spectrum. The absence of these in the existing observational data (for example, Ly-a) provides a bound on the mass. Beyond the bound, I will present a calculation framework for understanding the growth of structure where warmth and/or white noise are relevant. I will discuss nonlinear phenomenon (eg. solitons), resulting from the large initially isocurvature perturbations on small scales. Time permitting, I will include provide examples of growth of structure in multicomponent wave and particle dark matter.