For a foolproof casual option, you can never go wrong with this pairing of a long sleeve shirt and charcoal jeans. Feeling adventerous? Break up your ensemble by wearing black athletic shoes. Casual outfits for stylish older gents aren't actually that hard, as you can see here.
If the setting permits a relaxed menswear style, you can easily rock a long sleeve shirt and navy chinos. For something more on the casually cool side to complement this outfit, complete this outfit with a pair of black athletic shoes. So if you're after outfit ideas on what to wear as you slip into your 50s, this outfit is definitely worth saving for later.
This relaxed combination of a long sleeve shirt and black chinos will attract attention for all the right reasons. For footwear, go down the casual route with black athletic shoes. Now that's how you do semi-formal as a mature man.