Yes, your Dad must have been pretty flexible if you had a worldly girlfriend in high school, and they were OK about it. My daughter had a JW bf, which is how I got involved in this forum. His mother gave me an Awake (dated Jan 22, 2001) which said no dating till you are ready for courtship and marriage. There is also a lot of information in the "Questions Young People Ask" book on that same topic. She was very honest about saying that no matter what age the kids were, my daughter would not be acceptable because of the religious difference (which made sense to me, I didn't want her to marry a JW, ever).
Since then I found this:
From the October 1 1974 Watchtower:
Is there any real objection to one of Jehovah's witnesses "dating" a non-Witness who respects the Christian's beliefs?-U.S.A.
The Bible does not comment about "dating," as this is a modern practice, but it does contain guiding principles.
Devoted Christians do not consider "dating" simply as recreation. Instead, they look upon it as an aspect of courtship, a serious step toward marriage. As to marriage, the Scriptures encourage selecting a mate who is "in the Lord," a believer, and not just a person who 'respects one's beliefs.' (1 Cor. 7:39) Hence, one who dated an unbeliever with a view to finding a marriage partner would be acting contrary to the Bible's admonition.
Then, too, while some unbelievers may respect one's beliefs, they themselves are not following the counsel of God's Word. This being the case, they may be inclined to take certain liberties with one of the opposite sex. Not being immune to the desires of the flesh, a Christian might yield to temptation when with an unbeliever. "Do not be misled," cautions the Bible. "Bad associations spoil useful habits."-1 Cor. 15:33.
Even if immoral conduct is avoided, an unbeliever is not a good associate. A person who is not a devoted worshiper of Jehovah God could not be a source of real encouragement to one who is. An unbeliever, while appearing to be a 'good person' and respecting the believer's faith, still does not appreciate spiritual things. Lacking a spiritual outlook, he or she would not strengthen the believer in a determination to be faithful to God. On the contrary, since the unbeliever may be thinking of marriage, he would be encouraging the Christian to disregard God's counsel about 'marrying only in the Lord.'
It is therefore wise for a dedicated Christian to look for possible marriage mates only among those who are believers and who possess spirituality.-Compare Deuteronomy 7:3, 4; Nehemiah 13:26, 27; Malachi 2:10-12
I have no idea if people have been DF for dating normal people, but I would guess, yes, especially if the elders suspect an intimate relationship.