In Engpsh, you can describe the difference between a person's actual age and their appearance as follows:

"They look younger/older than their actual age."
"They don't look their age."
"They have an ageless appearance."

For example: "She looks much younger than her actual age. People are always surprised when they find out how old she is."

Alternatively, you can simply describe a person's appearance and mention their age separately: "She looks quite young, but she's actually in her mid-40s."