LXV
Letters are not numbers. Not all letters in the alphabet represent Roman numerals though some letters do.
XXV-VI
You could use roman numerals but then you would need 6 letters: XIII-V-XI.
Today we would write it out as XLV
MMMCLDXXVlll
Not possible ! Even if you were to use Roman numerals, it would be XIV-VIII-MMXIII
First write the birthdate as a number so that, for example, a date like 12th October 1537 would be written as 12-10-1537. Then replace these three numbers with the correct Roman numerals. In this case the Roman numerals would be XII.X.MDXXXVII
5909 in Roman numerals would be (V)CMIX
You cannot write it in 5 letters, you can write it in 4. Using roman numerals it would be: IX/V/MMXI, this required 4 letters.
In today's modern notation: XVI-XI-MCMXXXVIII
Just use the letters I V X L C D and M
Even if you used roman numerals, it would still require more than 5 letters.