Go for a simple yet refined option by combining a shirt jacket and a dark brown v-neck sweater. A pair of dark brown suede brogue boots is a good choice to round off your getup. As you're moving from your 20s to your 30s, you probably want to start dressing like an adult man. In this case, inspiration like this comes in useful.
Dark Brown V-neck Sweater with Shirt Jacket Outfits For Men In Their 20s
This combination of a shirt jacket and a dark brown v-neck sweater looks refined, but in a modern way. This look is complemented wonderfully with dark brown suede brogue boots. If you're working your way through your late 20s, take cues from combos like this to take a more adult direction in your style.