That system is doesn't exist.

Wrong MMO. But you can Tag two characters together to gain XP without having to level up both separately.

I am fairly certain BDO has never had this type of system that you mention, but there is a way for a high level player to level a low level player. If you mean select a lower level player, like another person, you can join the party of a higher level player and gain EXP with the high level player grinding. This is called powerleveling and I only recommend it to players who have already completed the main questline once, or a more experienced player. Alternatively, like Eriane mentioned, if you meant a low level character on your own account, then you can just tag it to your higher level grinding character to get the exp on the low level one, but you must be at least level 7.