English Translation
He is a thirty-year-old bachelor.
“Er ist ein Dreißigjährigerunggeselle.” Does that work?
He is a thirty-year-old bachelor.
“Er ist ein Dreißigjährigerunggeselle.” Does that work?
Yes, that would kind of work, but it needs to be two separate words: dreißigjähriger Junggeselle.
Just be aware that it becomes ambiguous if you phrase it that way. It could also mean that he has been a bachelor for 30 years - kind of the “eternal” bachelor. It’s similar to “der dreißigjährige Krieg” - a war that lasted for 30 years.
Another, unambiguous way to phrase it is to include “Jahre” and make it close to the english sentence:
dreißig Jahre alter Junggeselle.