DataFrame Minmun Size

Hi



If I will like to create a classification model using RandomForest and XgBoost for EURUSD in a 5 min timeframe, how can I determin the minum DataFrame size in terms of rows or dates or number of trades? 



Days a go I trained a model over 1800 rows that worked very good in a 1 month period but in a year the results where completely oposite