It might be more accurate to say that people who have Gilbert's are often jaundiced.

There are loads of causes of juandice. Some of them are really bad news.

It can be pre hepatic (like haemolysis), intra hepatic (like Gilbert's) or post hepatic (like gall stones).

Other things that you'd have to consider would include drug reactions, pregnancy, biliary obstruction, autoimmune causes (haemolysis, hepatitis...) Other causes of hepatitis (viral, anaesthetics, alcoholic...), I forget the rest of the list. It's not hard to find out you want to know the other causes.

The most likely causes are also different at different ages.

Gilbert's is one of many.