When you have more experinece in programming in more languages, you'll find that in a lot of modern languages an int is always 32 bit and a long is 64 bits

Once you gain some more experience you will realize that ‘a lot of’ is not good enough. Some languages do, some don’t. If you define a format, you don’t say ‘int’, you say something like “int32 in network byte order” (a.k.a. big endian).

Interesting that you were boldly claiming that experts use a dd-MM-yyyy format

Stop being willfully ignorant. I’ll repeat it once more: my claim is that you should store your dates as individual components, not as a the time since an epoch. I don’t care how those components are stored as long as it’s clearly specced.