A suit looks especially refined when teamed with a navy dress shirt for an outfit worthy of a modern gentleman. If you don't want to go all out formal, complement your outfit with mustard loafers. A good source of inspiration for those looking to move their look towards maturity.
Mustard Loafers with Suit Outfits In Their 30s
This is hard proof that a suit and a navy turtleneck are awesome when paired together in a refined look for a modern dandy. Add mustard loafers to the mix and the whole ensemble will come together. This outfit is most probably what you're looking for as a 30-something guy.