The 70-year-old actress is "shocked" she has reached the milestone, which she has described as a "strange moment" in her life, and she has claimed the "secret" to having younger-looking skin is "staying engaged", being inquisitive and to have a "good time" without smoking.
The flame-haired beauty told Vogue.co.uk: "I'm shocked to be 70 myself! I keep thinking I'm younger, and I feel that inside! It was kind of a strange moment, that milestone.
"The secret - I mean, honestly, I think staying engaged and staying curious and having a good time is really a lot of it. And not smoking is really important."
The 'Stepmom' star also think staying hydrated and avoiding anything too extreme has benefited her complexion, as well as genetics.
She added: "I think that staying hydrated and not doing anything too extreme, too... Also I'm not really a drinker. I think a little bit of wine in moderation is probably good, but I think really if you drink heavily it's not great. But I guess good genes. I thank my mother."
The L'Oreal spokesperson regularly asks the cosmetics company to send her new products to sample, although she relies on the brand's Age Perfect Golden Age Soin Jour Rose moisturizer.
She said: "For me a lot of it is all about moisturizing. The new L'Oréal Paris moisturizer - Age Perfect Golden Age Soin Jour Rose - is so luxurious. I'm really fond of that. As you get older the key is that it really penetrates but isn't greasy.
"That's a great advantage of working with L'Oréal, to be able to see things when they first come out. I always ask them to send new things my way. A lot of the lipsticks are really beautiful, really fun colors. I love the one that I've been wearing here in Cannes."