Together from the start..

[Niwashi]

hey can be a paladin and then after i lv.50 and i just change to red mage??

I believe so. (Though I have to admit I haven't kept up with all the announcements regarding the next expansion, so I could be wrong.)

while on the progress im not adding my attribute to the paladin, instead of give all to int?

Each class has it's own set of bonus attributes, so you can add all your GLD/PLD attribute points to Vitality, and still be able to add THM/BLM attribute points to Intelligence, CNJ/WHM points to Mind, ARC/BRD points to Dexterity, and so on.

The only one that presents something of an issue is Arcanist, since the points are divided according to the base class rather than the job, and Arcanist can become both Summoner (which still uses Intelligence as its primary stat) and Scholar (which uses Mind). You can either pick your favorite between SMN and SCH and assign all your ACN/SMN/SCH bonus points to that job's attribute, divide them equally between both, or keep using The Keeper's Hymn to reset them back and forth.