My Dad's too old for a navy blazer 
The "uniform" for men of 25+ seems to be skate trainers (NOT navy blue from M&S) or Converse, straight cut jeans, slogan tshirt (DP loves his De La Soul one I got from Primark, and he normally wears designer!) with, possibly, a short sleeved check shirt on top. Smartish military shirts look good on Dad, who is slight of build, but awful on DP who has broad shoulders.
I guide my Dad (youthful looking 64, into bands, most friends are 20 or more years younger) and he wears the above, like his mates. I will not allow him to wear skinny jeans, they make him look like his 30 year marriage to my mother is a sham
but he has been known to purchase a slight bootcut then wear them down the garden or fixing cars 46yo DP approves. DP also likes coloured jeans/linen in summer and owns more shoes than me - his cheapest pair cost more than my most expensive pair
which tend to be lace up brogues, MBTs in trainer styles...
Avoid: Hoodies, skinny jeans, anything baggy, flat fronted trousers, white socks (trouser hem should meet sole of shoe), tucked in shirts, anything navy (including blazers and vomit-inducing skate-style trainers from M&S), ALL sportswear (unless actually taking part in a sporting activity) and anything too obviously fashionable like trilby hats.
HTH 