Start with a good hair cut, that alone can take years off. Second, a decent bra in the right size, many threads in here on how to get the correct size and fit. Third, find out what colours really suit you best and wear them. fourth, find out your true body shape and what styles suit your shape. Does any of that help?
It's not always about looks either - it may also be about how she carries herself, her demeanor, her attitude, etc. Sometimes youthfulness is intangible, and difficult to cultivate, and it ain't necessarily something that the youthful person is even aware of.
I've been told this (about myself, i'm 39) all my life. It's often been frustrating, weird, flattering....but I'm mostly nonplussed. I don't dress or act younger, and I can sure as hell see the changes that have occurred in my face, skin and body over the years, but people still make some pretty weird comments about it.
Can also be about face shape and features: larger eyes, lip shape, etc. I don't feel like I'm explaining this very well, but I guess I'm saying when I've noticed this in other people it isn't something clothes and makeup seem to alter. Nor is it about weight. Some of my relatives who are in their 70's look much younger than they are, and it isn't down to clean lifestlyes and slenderness! Genetics, perhaps.
Anyway, enjoy 43, nothing wrong with looking that age!
Agree with Toasted.... My sister is 18 months older. I was always assumed to be the eldest as I'm more reserved and my big sis is out there, barking at the moon! I do look younger now but that's because we are 50+ and I'm the one that's used high SPF due to various allergies. So, now, I have fewer wrinkles.
I'd say yes to a decent hair cut. Maybe some colour to add brightness and "lift" your face? For me, weight gain (menopausal) has been ageing. It's tough losing even 10lbs now where before, it'd drop off if I did a bit more exercise. Metabolism has changed! So, stay trim, exercise, lots of water but essentially, it's about genetics, really.
Yes, my male friend is 54 and hasn't one wrinkle on his body yet, not one grey hair, has remained as tall and handsome as when young. His skin has a subtle, lovely glow, his hands are elegant and unlined and his hair is silky and enviably soft. What gives??? He smokes, drinks occasionally, buys his meals from the bloody chippy 4 nights per week, suffers anxiety and depression and never drinks water. His dad was similar and lived to reach 96.