“Ravenous” usually is used simply to describe a person directly and almost always related to hunger for food. “He was ravenous after his long fast.” “Voracious” needs another noun to describe the person. “He was a voracious reader”. You wouldn’t use “he was voracious “ alone unless what he was voracious about was clear from the context.

They’re very similar and can mean the same thing when they’re referring to hunger. Ravenous is very hungry. Voracious is wanting or consuming large quantities. The difference is in how voracious can be used for things other than food. “He was a voracious reader.”