Jesus existed before being on Earth. Agan I must bring up Enoch

The angels, when they took the oath to fall on the Creation of the Earth were overjoyed at discovering (through the oath, came part and parcel with it somehow) the name of the Messiah. He's also talkd about as the 'Elect One' judge to mankind in the final judgement, etc. He was also there in Eden.
The word Elohim (which was the word used for God in the beginning of the Bible, and especially at Creation) is plural male and singular female in gender. God and Jesus being the two parts male, and the Shekinah, which is the Holy Spirit is female in gender in the Hebrew language making up the singular female. So, the Trinity has ALWAYS existed, but wasn't clarified until Jesus (Yeshua) explained it.
Now, as for why God took so long.....it was obviously planned, and it was foretold. If it had have been further back in history it may not have been documented the way it was, further forward in history, and people may have given up hope of the Messiah coming and not taken much notice. Who knows, these are just some possibilities lol.