How can I prevent age spots?

The answers here are great, and I'd like to echo them.

As Lori stated, many topical lightening agents contain Hydroquinone, an agent which has not been approved for long-term use. In our practice, we really only recommend its use for three months or less. Other agents, such as kojic acid, are safer but still may be irritating.

The Cosmelan treatment can definitely help correct hyperpigmentation, as can Photofacials or fractional laser resurfacing. Some hyperpigmantation may be due to melasma, a condition which is very difficult to treat. Women who are pregnant or taking birth control pills are most at risk. It may be hereditary.

There is no easy, fast, cheap way to correct brown discoloration due to melasma, sun damage, or irritation from cuts or pimples. Melasma may be chronic, so if your physician's diagnosis is melasma, you will always have to be careful to avoid conditions that may aggravate it. So prevention really is key here! I cannot stress that enough!

Wearing a good, broad-spectrum sunblock of SPF 30 or higher during the day is important. Look for formulas that contain zinc oxide and/or titanium dioxide, and reapply frequently if working outside. Wearing mineral makeup like Jane Iredale will also boost your sun protection. Quit smoking, or don't start. Eat a balanced diet, and drink plenty of water. Wear a wide-brimmed hat. Use a topical anti-oxidant serum (like l-ascorbic acid) during the day, and a retinol cream at night. These ingredients cannot only prevent and somewhat correct damage, but also discourage the bunching of melanocytes.

Taking good care of your skin now not only prevents age spots, but wrinkles and skin cancer as well. You don't have to spend life under a rock, but be sensible. Your body makes those brown spots as a protective sheild. Essentially, your skin makes a tan to shade some damaged/delicate or irritated cells from further assault. If you see brown spots starting to appear, consult a professional to help you understand the cause and develop a treatment and/or home-care regimen that will work for you.

All of the recommendations by the panel are a good starting point.
Prevention is always the key concept when taking care of your skin.
The next issue would be how to treat sun/age spots once they have developed. Many of our patients come to us after having disappointing results using hydroquinone/bleaching/fading creams. Also, these products are not meant to be used beyond 3 months. Another good option for treatment would be lasers which is very effective for all skin types. We also have been using Cosmelan with excellent outcomes. Cosmelan is a depigmentation mask with little to no downtime. Both treatments provide good options.

1.  Daily application of a UVB/UVA sun blocker

2.  Avoid the midday sun

3. Wear a wide brimmed hat

See a dermatologist frequently and get rid of any spots that you have. Use high (eg. 50 or higher) spf with UVA protection in it.

Try to use brighteners on these areas if you notice spots forming.