The 39-year-old actress detailed her feelings for the 54-year-old actor in a recent interview with Esquire. Theron and Penn were longtime friends before they started dating, and the star said they built their relationship on a mutual respect and love for acting.
"It's nice to be in something where the friendship came first," she said. "There's a foundation of 20 years that the two of us have shared with each other in all these different ways that is really the foundation of something that has brought a lot of beautiful things into my life."
"I love the possibility of anything," she said of marriage, "but I'm really enjoying myself and the everyday moment and how that coincides with my son and my life and my friends. I'm a very, very, very lucky girl. Very lucky. He's hot. He is hot. How do you say that in an interview? You're a 40-year-old woman sounding like a 16-year-old."
Theron and Penn were first linked in January 2014, and confirmed their relationship in May. The twice wed actor previously told reporters he would consider Theron his first "real marriage," and declared the actress the love of his life in February 2015.
Theron dated actor Stuart Townsend for nine years, and adopted her son Jackson in 2012. Penn was married to singer Madonna from 1985 to 1989 and actress Robin Wright from 1996 to 2010, and shares daughter Dylan and son Hopper with Wright.