how old do you have to be to rent a car in europe?

I'm planing a trip to portugal and I need to get from lisbon to faro one day...its about a 5 hour drive. Any ideas? I'd LOVE to rent a car and rip it down the coast, but IDK if i'm old enough (or if insurance will be nuts)

otherwise I'm looking at a train. thoughts?

have a funny for your time