I am running some Monte Carlo simulations with GBM on time series of commodity prices. First of all, the price data is annual between 1900-1950. I would firstly like to know if it is bad practice to apply GBM simulations on annual data, as normally, daily stock prices are used.
Furthermore, since the GBM log-returns are normally distributed, I would like to know if this fact requires my data (that is the estimated annual "log-returns" of the commodities) to have a normal distribution.
I am doing Shapiro-Wilk tests to see if this is the case. However, I am uncertain if it theoretically is required to have normally distributed data to apply GBM if I want reliable results.