When a guy is 14 the criteria is usually: alive and not previously male.
When a guy is 18, she may need to at least have a hot body. Previous criteria still apply (the general trend is towards harder to please in life).
When a guy is in his early 20s, she may actually need to have a pretty face to cut the mustard.
Eventually she'll even need brains, and be fun to talk to.
These are all wild generalizations but the point is that it's different for each individual and even then different at different stages of their lives but physical attraction (beauty) is a big part for most people, as is being enjoyable company.