I have a historical dataset with teenagers' birthday in the format of dd.mm.yy, while they were all born after 1980.

e.g.
15.03.88
02.06.95
...

The variable name is: dob

I wrote the following syntax, but returned with empty values, it seems nothing has been converted:

gen dob_new = date(dob, "DMY")
format dob_new %tdDD/MM/YYYY

I also tried the following:

gen dob_num = clock(substr(dob, 1, 2) + "/" + substr(dob, 4, 2) + "/20" + substr(dob, 7, 2), "DMY")

It works but I don't know how to convert it back to dd/mm/yyyy format.
Could anyone please help?