In Asia in general it's not considered as “creepy” to have an older husband.
Women and society here tend to be much more practical about those matters. But from an evolutionary biological perspective, males always want to mate with younger females.
All that to the side, “many” expats are not really that much. It turns out that statistically the age gap in south-east Asia is just under 3 years.
So “most” expats are actually not that much.
Also, Thai women might be looking quite young at an older age, so there is an impression that the age gap is large, when in actuality, it is not.
Finally, most women want a man that is just a few years older than them.
A good rule of thumb is "half + 7 years". Meaning, the person you are in a relationship should be at least half your age + 7 years old. This means if you are 50 years old, you should date someone at least 32 years old.