For an outfit that's very easy but can be modified in plenty of different ways, try pairing a grey turtleneck with sweatpants. Go down the casual route with footwear by rounding off with grey athletic shoes. Dressing inspo like this will help you stay incredibly fashionable while getting into your 30s.
When the setting allows a laid-back getup, you can easily opt for a grey turtleneck and sweatpants. Bring a dash of class to your look with black suede chelsea boots. Ensembles like this have a refined air that suit 30-something gentlemen very well.
Rock a grey turtleneck with sweatpants for a casual kind of sophistication. Take this look down a dressier path by finishing off with a pair of black leather chelsea boots. If you're wondering how you should dress as a 30-something, this ensemble gives a proper idea.