This combo of a grey crew-neck t-shirt and grey jeans gives off a casual and effortless vibe. Unimpressed with this getup? Invite dark brown leather casual boots to change things up a bit. You might be thinking that just because you need to get bundled up you have to sacrifice smart style, but it's just not true, and this ensemble is a shining example. Casual ensembles for 20-year-old gentlemen aren't actually that hard, as you see.