"aged below" is correct and usable in written English.
It can be used when referring to someone's age relative to a certain age limit, for example: "Children aged below 18 are eligible for the program."
There was no suspicion the girls were aged below 16.
The new wage won't apply [pdf] to about 11% of the workforce who are aged below 25.
In India, some 60% of the population will soon be aged below 34.
Nearly 50%% of the population is aged below 15.
Women aged below 15 and above 45 years were excluded from participation.
In the Netherlands Focetria was the predominant vaccine, but Pandemrix was used in children aged below 6.
Responders aged 30 or more were approximately 60% less satisfied than those aged below 30 (Table 6).
Any worker aged below 18 should be clearly identified, the company adds.
Typically involving girls aged below fifteen years of age, this traumatic procedure may involve removing, stitching and cauterising the genitals.
This group added almost twice as many people to the overall numbers as the group aged below 20 did.
A third of problem gamblers, those whose addiction causes serious disruption or harm, are aged below 30.
