This combination of a cable sweater and a grey short sleeve shirt is irrefutable proof that a safe casual ensemble can still look really interesting. Introduce a pair of dark brown leather desert boots to the mix for extra style points. Can you see how super easy it is to look sharp and stay toasty when cooler weather hits, all thanks to ensembles like this one? And if we're talking casual outfit ideas for men in their 30s, this getup looks good on most gentlemen.