Can everyone, no matter the age, get gynecomastia?

Yes. Males only. Very rare prepuberty. Most common in males middle aged and above. Seen in younger males, especially if taking body building hormones or smoking lots of pot. A large percentage of gynecomastia is idiopathic i.e. We don't know for sure what caused it.
Yes. Yes, males of all ages ( after puberty) can present with gynecomastia. If symptomatic and/or aesthetically displeasing, surgical correction of gynecomastia can be worthwhile. Treatment is individualized depending on the specific patient's situation; involves direct excision of glandular tissue, liposuction surgery, and/or occasionally excision of excess skin as well.