When you were younger, the air was less contaminated with organic compounds, which will have a more general scattering spectrum (making the sky more whitish). I think higher humidity has a similar effect. It also depends on time of day. Nearing sunset or sunrise there is a spectral shift in the skyshine that will give the sky a whitish quality. There is a gradual transition from blue daylight to reddish-orange sundown/sunrise light and white lies in the middle.