First thing, welcome to Tropical Fish Keeping forum.
Second thing, I have moved your post to start its own thread. You had posted in an existing thread that was un-related.
Third, to the angelfish. Lifespan is stated to be anywhere from 8 to 15 years, with 10+ the usually average. So this is not likely age. Also, at maturity, it will be 6 inches body length, which this fish does not appear to be yet. [Before I go on, I will refer you to our fish profiles, under the second tab from the left in the blue bar across the top of the page. Lots of info on each species there, and this one is the Scalare Angelfish
or scientifically Pterophyllum scalare
. When the name is the same in posts as in the profile it shades, and you can click on it to see that profile.]
Diagnosing trouble is not always easy. This could be a genetic defect, health issue, stress. The latter can be caused by many factors, including water parameters, water conditions, aggressive fish in the tank, lack of other angelfish, etc. Some of these will be mentioned in the profile, so I won't repeat here.
Do you have numbers for the water? As the fish was OK for 4-5 years, has there been a recent change in pH or temperature? Are ammonia and nitrite zero? And what are the nitrates?
You list some risky fish as tank companions; have you seen any sign, however slight, of other fish pushing or chasing the angel, or the angelfish turning away from other fish? Even if no physical contact occurs, just the presence of something "nasty" can stress out the angelfish. And a fish like the Serpae Tetra
can be deadly with angelfish.