A dark green crew-neck t-shirt and sweatpants are both versatile menswear staples that will integrate wonderfully within your daily off-duty wardrobe. And it's a wonder what black slip-on sneakers can do for the outfit. Rest assured, this outfit will keep you toasty as well as looking seriously stylish in this awkward transition weather. This pairing should clear any doubts you had about wearing casual clothes as a 40-something man.