You should focus on openings that require thematic or strategic understanding, as opposed to ones that require lots of book-knowledge/theory. Then you will get to positions that you are comfortable in and not have to learn the nuances of sharp and highly-analzyed variations that more experienced players will tend to thrive in. Basically, an experienced player's "comfort zone" is beating a less-experienced player in a theoretical line: they have a risk free way of leaving the opening with an advantage. If you take away that theoretical advantage, I would argue they will be less comfortable facing you.
IM Andrew Martin discusses opening repertoires here. Based on the above, from his list of opening repertoires I would then suggest:
For White: Trompowski and Pseudo-Trompowski
1 d4 Nf6 2 Bg5! And 1 d4 d5 2 Bg5! A must here will be to get hold of as many Julian Hodgson games as possible- he has been carving up Patzer and Grandmaster alike for many, many years. At the heart of this repertoire is the limitation of Black's choices- you are conducting the game on your terms. The positions can be different too- White can opt for Pawn structure play or outright attack depending on how he is feeling.
For Black: Scandinavian and Slav set-ups
Rock solid. As Black vs 1 e4 play the main line BANKER with 1...d5 2 exd5 Qxd5 3 Nc3 Qd8! or 3...Qa5, in both cases following with ...Nf6, ...c6 and ...Bf5! And vs d4 and Flank Openings go for the solid Slav set up with ...c6 and ..d5, aiming for a similar structure. Truly an opening which can be learned in a minimum of time .
