Jewelry marketing is very life-cycle oriented, and it is the goal of jewelry marketers to "connect" with a customer early in their lifetime and to remain their jeweler of choice throughout their lifetime.
For a jeweler, a male customer's life-cycle might look something like this:
Younger consumer - small gifts for girlfriend
Slightly older consumer - engagement ring, holiday gifts
Slightly older yet - Bridal ring, holiday gifts
Maturing consumer - watches, anniversary gifts, holiday gifts, Consumer with children - birthday presents, holiday gifts, Sweet 16 gifts, bar mitsvah gifts and First Communion gifts
So, you can see how reaching a consumer earlier in life offers the potential to make more sales to that customer than reaching them later in the life-cycle.
Life-cycle stages effect most other businesses, too. As one grows older, they tend to earn more money, live in better house, drive fancier cars, have children (new consumers) and take on other responsibilities. All of which impact and influence their purchasing behavior.
Companies that offer products that appeal to certain demographic groups cannot afford to utilize a one-market advertising or promotional strategy. Take something as basic as breakfast cereal: while it may be fine to appeal to children on the basis of offering sweetened cereals in funny shapes with animated cartoon characters, older adults may be more sugar-conscious and concerned about controlling their weight and overall health. So, even though you'll find Sugar Pops and Grape Nuts on the same aisle at the grocery store, each is targeted to a totally different demographic.
I hope my rambling has helped.