you didn't use the standardized data (X_std) for splitting into train and test subsets

[higherdim]

In your code, you didn't use the standardized data (X_std) for splitting into train and test subsets. You used the original X data. Typo?

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Separating X vs. y dataframes

X_std = pd.DataFrame(std_scaler.fit_transform(X), columns=X.columns)
y = healthy_df['age']

Separating dataset into train and test subsets

X_train, X_test, y_train, y_test = train_test_split(X, y, test_size = 0.33, random_state = 42)
`