So long as they have stayed frozen all the time then many 10s of years. I have made dna from many hundreds of stored bloods which were over 20 years old and the dna was still suitable for southern blotting

DNA is very stable so you can preserve your samples as long as you can in a frozen state and I prefer to keep them in aliquots 200µl each and after DNA extraction it will be okay. During my master, I stored many samples for more than 2 years and after extraction, it gave a high yield of DNA and subsequently very good results.

but I prefer to extract DNA at first the store it for many years

As much as you can store at -20 degree freeze.