Given the choice between the two sentences in your question:
Sentence 1:
"Every father behaved very boldly before they[*] got married."
Sentence 2:
"Every father behaves very boldly before they[*] gets married."
*There is another issue here, besides the one you're asking about. The subject, verb and pronoun in your sentences don't all agree in number. This stands out more in the second sentence than in the first, because of the 3rd person singular and plural forms being distinct in the present tense (gets vs. get). Please refer to the bottom section of this answer for alternatives that fix this problem too. As it currently stands, the second sentence in particular is not idiomatic - a native speaker would not use that phrasing.
You are correct that the second sentence (the one using the present tense) implies a general statement, while the first (which uses the past tense) refers to specific, past events. As matter of fact, to most [all?] listeners, your first sentence cannot be a general statement, and can only refer to something that actually happened prior to now.
Reading your second sentence, one gets the impression that it is meant to refer to the actions of fathers in general (real or hypothetical), and not just to some particular individuals at a given time.
Your first sentence does not convey this same level of generality. Instead, the reader would think you were talking about the actions of a specific set of real people (who happened to be fathers) at some definite time in the past.
The difference in signification between the two sentences is due to the difference in the tenses you use. The simple present tense is the one which is most commonly used for statements of general truth in English. According to this source: https://academicguides.waldenu.edu/writingcenter/grammar/verbtenses, "the simple present ... describe[s] a general truth or a habitual action," while "the simple past tense ... describe[s] a completed action that took place at a specific point in the past." Note, however, that the simple present is not the only tense that can be used for general statements: the future works as well (see the comment by FumbleFingers under this answer for an example of a future tense general statement).
If you intend to make a general statement, you should definitely choose the second sentence over the first.
If you're looking to express the same idea as in Sentence 2 using a different tense, you might say:
Every father will behave very boldly before he gets married.
Although this isn't directly related to your question, there are also number agreement issues in both sentences. The word "every" is grammatically singular, even though the meaning being expressed is plural! If you want a (both grammatically and semantically) plural subject, you should use "all" instead of "every." (Reference: https://www.ef.com/wwen/english-resources/english-grammar/using-each-and-every/)
Example (plural subject, verb and pronoun):
All fathers behave very boldly before they get married.
Or else, if you want to keep "every," the pronoun should be singular too:
Every father behaves very boldly before he gets married.
Another alternative would be to avoid the issue altogether by rephrasing:
Every father behaves very boldly before getting married.
