If you're looking for a younger Asian wife, then probably the best place to head for is the Philippines. Large numbers of Filipinas like the idea of finding a husband from overseas. Filipinas make great wives. Filipino people are used to living overseas, and as many as 10% of the population already do so. Many Filipinas speak English, and if they don't it's much easier for them to learn English than it is for a Chinese or Thai lady to learn English. Another great thing about the Philippines is that the majority of the population is Catholic. Marriage is taken much more seriously than in Thailand or China, and Filipinas are looking to marry for life.
Sign up to any Asian dating site and you'll be bombarded with interest from young Filipinas. Whatever age you are, you'll probably receive a lot of interest from 20 year old girls.
While all this attention is flattering, just be aware that marrying a much younger lady can be hazardous. Here's a useful age difference suitability calculator to see if your Asian wife may be too young for you. It's worth bearing in mind that Filipinas do tend to prefer older men than do Asian women from other countries such as Japan, China and South Korea.
By all means don't avoid the younger ladies. However, bear in mind that the under 25's are far more likely to be scammers. They are often much less marriage orientated than older women, so dating them can be much more stressful.
Good luck with your search for a Filipina wife.