Adjectives are classed as :1) fact adjectives and 2) opinion adjectives.
Fact adjectives give us factual information about age,size, colour etc.
Long/short; young/old;hot/cold are fact adj.
On the other hand, beautiful/ugly;interesting/boring, are opinion adjectives.
Opinion adjectives go before fact ones.
When we use two or more fact adjectives like in your first case, we often,but not always, set them in this order:
1) how big? 2) how old? 3) what colour? 4) where from? 5) what is it made of?
So it would be correct to say: friendly fat young man.
Fat/round/thin/slim/wide are shape and width adjectives, while big/small/tall/short/long are size and length adjectives.
I hope this helps.