How do I calculate birthdate from the age at test date (ageIGA) and the test date (tvdIGA)?

Variables are below

dataex tvdIGA ageIGA

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Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input int tvdIGA double ageIGA
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
19588 10.4
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21135 14.1
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
21268 12.3
19678  4.7
19678  4.7
19678  4.7
19678  4.7
19678  4.7
19678  4.7
19678  4.7
19678  4.7
19678  4.7
19678  4.7
end
format %tddd-Mon-YY tvdIGA