Can be hard to decipher, but it can be a natural thing, younger girls wanting someone more mature and settled. And then there is such a thing as chemistry, which is age- and genderless, though taking laws and common sense into account. At 21, a girl is a woman, or at least at the stages of womanhood. So 30's/20's to me isn't off the mark. You can be the grounded force that settles her life. But of course .. she can get tired of it at 25-30, wanting to live more again and break free. There is never any guarantees. You may also want someone more mature when that time comes.
But back to the chemistry thing. You know when you think about mick jagger and his current wife, what, close to 50 years younger .... i'm not going to believe that is genuine. Even if he is a nice guy. Even still, there is a small percentage chance it is. But money and instant fame has been a motivator for many women across the ages. As sad as that is.
To me, it bottoms out in astrology. If the energies matches, there is a higher chance for it to work long-term. I'm then thinking about the ten first placements, not just the sun.
But one also has to take into account certain things, like any close relative during childhood. If one has had a strong precense of certain energies, one may be opposed against such energies in others, even if it is an energy one harmonizes with. It depends on how things has been.
Therefore, the most important thing for everyone, is to familiarize oneself with one's birth chart, one's own energies, and try as well as possible to rid oneself of any bias. That can be difficult. But if one manages that, one can increase the chance to understand and even embrace the different/difficult/disharmonizing energies the other person has. Both should do it, but if the chemistry is strong enough, one can of course tolerate and live with some disharmonizing energies. As ever, it all depends on the depth of understanding.
have birth charts helped your dating life?