In my opinion, "middle age" these days are 60+, I am not in that group yet.
In my group of old friends since high school, some look exactly like 30+ years ago. Some gained so much weight that no one can recognise anymore. Some loss a lot of hair. Some has whole head of white hair.
Some are worn out by life - you can see it in their face.
Some remain young at heart...
But overall, I find that the more positive my friends feel, the younger they look.
Make sure we have enough money to use for retirement, then you will have a lot less worries.