Looks like this was recently expanded to 10 years in the past and 1 year in the future: https://cloud.google.com/bigquery/docs/streaming-data-into-bigquery#time-unit_column_partitioning

Time-unit column partitioning

You can stream data into a table partitioned on a DATE, DATETIME, or TIMESTAMP column that is between 10 years in the past and 1 year in the future. Data outside this range is rejected.