German words ending in -ling

-ling turns an adjective or a verb into a person or a thing. Lehren gives der Lehrling, früh gives der Frühling, lieb gives der Liebling, feige gives der Feigling. Whatever it is built from, the result is masculine.

The suffix has no exceptions. The gender belongs to it, not to the person or object the word describes, so a female apprentice is still grammatically der Lehrling. That is the same mechanism as the diminutives, which make everything neuter no matter who they name.

What can catch you out is a different ending that happens to share the letters. German has borrowed a pile of English words in -ing, and most of them came in neuter: das Recycling, das Bowling, das Training. Not all. Der Smoking is a dinner jacket, der Pudding is masculine, die Holding is feminine, and each of those has to be learned as a word. What they share is that none of them was built with -ling: they are English nouns that arrived whole, so they are not exceptions to the rule above and should not be learned as any.

Listen for the tone as well. -ling often carries a slight edge. Der Schwächling and der Feigling are not compliments, and der Eindringling is an intruder. It is not always dismissive, since Frühling and Schmetterling are neutral, but the tone is there often enough to notice.