Pairing a shirt jacket with a grey long sleeve t-shirt is an awesome idea for a casual ensemble. You could go down the classic route with shoes with a pair of tobacco leather loafers. This pairing demonstrates how gentlemen in their 30s kill in the fashion department.
If the occasion calls for a casually refined look, you can easily dress in a shirt jacket and a black corduroy shirt jacket. Black leather casual boots complete this ensemble very nicely. Perfect if you're looking for some incredibly inspiring style for 30-something Millennial guys.
This ensemble with a shirt jacket and a grey long sleeve t-shirt isn't so hard to pull off and is easy to adapt according to circumstances. Introduce a pair of brown suede desert boots to the equation and ta-da: the ensemble is complete. Rest assured this getup is something you can totally wear as a gentleman in his 30s.