1)
What do we learn from "Ba Chetzron El Bas Machir? Lekachah v'Hu Ben Shishim"?
1.
'Rashi': All this is for the honor of David. Chetzron took her for a Pilegesh, without marriage, like "Ba El Bas Sheva." Chetzron was 60 at the time. These were two shortcomings - she would be only a Pilegesh, and he was old. Even so, due to the honor of Yehudah's family, [her family] gave her to him. And when Ya'ir was born, Bnei Machir gave to him 23 cities in order that Ya'ir will marry one of his daughters.
2.
Radak: "V'Hu Ben Shishim" applies earlier. When he was 60, he married her.
3.
Malbim: Initially, he had Bi'ah with her without Kidushin, After he was 60, he married her, after he already fathered Seguv from her.
