I have a 5 year old ipad, never used. battery does not charge up. do I need a new one?

If it’s 5 years old and hasn’t been charged all of this time it’s likely that the battery is bad and would need to be replaced (or you may need to consider buying a newer iPad). Do as suggested and see if it will power on after charging for 24 hours. Even if it does though it’s highly likely you would need to replace the battery.

Leave ii on the charger for, at least, a full 24 hours.

See if the battery in that iPad revives itself.

Best of Luck to You!