Mostly the context will show you the gender with such words as adulescens.
Sometimes Latin writers use the words mas (male) and femina (female) to say what the gender is. This is mostly used with words, used for animals, when there is only one word with a grammatical gender to denote the females and the males.
Exemplum: The word aquila is used for males ans females, but in the grammar it's always f. But if you want to denote it's a male, you can put: aquila mas and for a female aquila femina. Adjectives will then be put with mas or femina: aquila mas magnus, ...
But when you only use aquila, you have to say: pulchra aquila, which can denote a male or a female: the context will clear up this one.
When there is a word for the male animal and an other for the female animal: you don't have to use mas or femina off course: equus for a male, but equa for a female.
This is normally only used for animals. I think it can be used for humans too, but only in biological non-classical texts.
If you really want to denote the sense of words like adulescens, just use an other word. You can put in as an apposition and use the subject, to which it would be apposed, to mark the gender.