No matter where the day takes you, you can rely on this casual pairing of a black shawl cardigan and a white and black horizontal striped v-neck t-shirt. If you don't want to go all out formal, add a pair of blue camouflage athletic shoes to the mix. Nothing like a killer outfit to brighten up a gloomy autumn day. When it comes to casual outfit ideas for 30-year-old men, this combo looks good on most gentlemen.