Because in English "advice" is uncountable, so you can't put "a" before.

The word "advice" is an uncountable noun. Uncountable nouns do not have plural forms. They cannot be used with the articles a/an. You can use "some" before "advice": He gave me some advice. To refer to a single item of advice, you can use the expression ‘a piece of advice’: Can I give you a piece of advice?

Advice is an uncountable noun. advice | AmE ədˈvaɪs, BrE ədˈvʌɪs | noun 1 uncountable(counsel) consejos mpl; (professional) asesoramiento m ▸ a piece of advice un consejo

You can say "he gave me ten pieces of advice about girls" if you want to specify the number of tips. And don´t forget the 3rd person S: "That meanS": :)

Ok. That mean I can't say "He gave me ten advices about girls", for example?