Go for a pared down but classy ensemble marrying a brown cotton blazer and jeans. A pair of dark brown casual boots is the glue that will bring this look together. This ensemble is probably exactly what you're looking for as a 30-something Millennial guy.
For an outfit that's super straightforward but can be worn in a myriad of different ways, pair a dark green shirt jacket with jeans. Dark brown casual boots are the perfect addition for this look. Sport this outfit to pull together a more conservative look as a gentleman in his thirties.
This pairing of a white cable sweater and jeans combines comfort and practicality and helps keep it simple yet modern. Clueless about how to complete your outfit? Round off with dark brown casual boots to ramp up the classy factor. So if you're looking for a modern yet age-appropriate combo, you found it.
If you like a more laid-back approach to fashion, why not dress in a navy shirt jacket and jeans? Complete this ensemble with a pair of dark brown casual boots and the whole ensemble will come together wonderfully. If you're over 30, take cues from ensembles like this to add more maturity to your wardrobe.
As you can see, looking casually neat doesn't require that much effort. Just go for a brown lightweight puffer jacket and jeans and you'll look awesome. Introduce a pair of dark brown casual boots to the mix and the whole look will come together. Looks like this have a sophisticated air that suit young gentlemen really well.