Hey Fashintern. Referring to your pix of different necklaces, I think #9 fits the available space very well and complements, whereas some of the others fight with the top.
As far as what can or cannot be worn by "grownups": I believe you should dress according to your own individual personality, not your age! Too many women are surrendering to boring because they consider themselves too old or maybe not attractive enough to wear something they really love. Color is also something that seems to be avoided in conservative style...But, why? Color gives any woman radiance!
Styling according to your own likes (despite what others may think!) rather than what is offered to women of your age bracket, is what sets you apart and brings life to your look! ...AND, makes you feel better about yourself. Therefore, you are happier, giving yourself the added attraction of a smiling, contented countenance!
Wear the seasonal colors that complement your skin, hair and eye colors, and wear what YOU want to wear!!
P.S. I think chokers go best with tank tops, spaghetti straps, etc., in cases where the top doesn't interfere with the choker.
Blessings,
Cindy@diybohemian.com