The I used to look so young for my age Vs years later, darn I look too old for my age scenario is a common phenomena in ME.
At the start of the cycle of chronic disease, ME sufferers would initially look younger than the age matched peers for obvious reasons if they never go in the sun, don't work down a mine until 6pm, 6 days a week, or experience huge levels of stress. On that basis you may be pretty pleased how youthful you look.
However....
ME sufferers (severely affected) would eventually look older than their age matched peers for not so obvious reasons, and that is uncontrolled oxidative stress.
In my experience of having this condition as a kid, teen, then adult:
Meet an ME patient who is homebound for 5 years, and they'll likely look young. I was always amazed how young I looked in my 20's more like a teen. I had incredible skin, despite being ill. I put it down to avoiding sun, never smoking.
But then..... look in the mirror as a severe grade ME patient who is homebound for 20-30 years and you'll likely look like a long term smoker, even a drug user at times (dark circles/greenish tinge under eyes around face due to toxins), and looking 'infected' with blood shot eyes, dreadful skin, and wrinkles.
Why? Other than obvious reasons such as genetics:
At the end of the day, if you have a severe form of ME, and for a Long Time this chronic low grade inflammatory state (immune activation, cytokines, infections and eventual autoimmunity) is never treated.....then you will age excessively quickly compared to a 'healthy' person who doesn't smoke, keeps fit, avoids stress, and eats and sleeps well (emphasis on sleep) and who isn't undergoing all this free radical attack on your cellular DNA.
They way to 'prove' that long term, severe ME ages you badly, is other than seeing signs of premature ageing compared to your peers (wrinkled/loOse skin, grey/white hair etc) would be to:
Get a DEXA scan of your bones in your 30's and see if it's like a 70 yr old (Common in severe ME).
Get multiple blood assays for markers of oxidative stress. (Very high levels are common in severe ME).
Check your cognitive function for your age, and see if this is more like an elderly person (It will be).
Thus, if you're long term decade sick, untreated severe ME sufferer, then of course, you will be 'older' than you should be, much older and suffering from Osteoporosis, Arthritis, and 'Brain Fog' more akin to someone in their 60's, when you're 35+.
Conversely if you have moderate ME or CFS, then no, the effects won't be as pronounced and you'll probably still look pretty good for your age, considering you aren't well for a long time.