> Therefore I first split the data into training and testing sets at a ratio of 9:1, and selected the 25 most correlated features in the training set. Each of these features had a correlation with age between 0.83 and 0.94.

> The data was then split into training and testing sets at a ratio of 9:1, and fed into a sequential neural network.

What?? I thought it was split already.

(How training and test sets were obtained sounds fairly confusing. Did the author make sure there's no "data snooping" ?)