Rewatching buffy and can't believe their ages?

Rewatching Buffy in my 30s(I'm 32)and their ages confuse me because none of them look their age

Buffy (Sarah) was 19 at the time at first season yet to me she looks late 20s. She doesn't even look young enough for high school.

Faith(Eliza) was 16 at first appearance and she looks 20s. How is she 16?

Giles(Anthony) was 42 looks and sounds 50s.

Joyce (Kristine) was 41 looks 50s and even sounds 50s.

Miss calendar is 26 but looks and sounds early 40s.

Sorry just shocked lol. I had no idea