use advanced filter to filter character length

My first thought for something like this:

1) Add a helper column. It's not clear to me exactly what you mean by "rows over a certain length", but figure out what that means and add a column to calculate it. If it means "the length the text string in column A", then you can use the =LEN() function. If it means "the number of used columns in the row", then you can use the COUNT(), COUNTA(), or the COUNTIF() function.
2) Use that helper column as your filter criteria.