Aquamarine is a versatile stone. It comes in all different cuts (oval cut, emerald cut, etc.) and it looks great for young AND old-er ladies. For example, this 11+carat HUGE aquamarine ring would look great for a young lady, but large enough to satisfy a sophisticated (mature) woman looking for some serious bling.
Another great thing is that you can wear it during the daytime and it wouldn't feel too "heavy" because of its clear-blue-sky color. (But hey, some ladies love wearing chunky emerald rings or rich-blue sapphire rings in the daytime, so it just depends on the wearer).
This one in the photo with over 1 ct diamonds around the center stone is HK$31,000 or roughly US$4,000.