I posted this earlier and if you look at the wage band for ages of 35 - 39, almost 16% are drawing 10k and above. It tops up to more than 20% for the 40 - 45 age range for males before steadily declining.

So while the median is 4k, > 10k is not exactly uncommon at certain ages.

Personally, my gross monthly salary was around 5 ~ 6K by mid 30s and rising to >10K by end 30s. I was lucky; a door closed on me which lead to new doors opening and my salary jumped significantly within 3 years.