Angels being immortal (Luke 20:35-36), would be the same in the New Testament times and the Old Testament times.
There are several recorded instances in the Old Testament of angels being mistaken for men, therefore I conclude that angels would be similar in height to people.
Some examples of angels being mistaken for people:
Three angels appeared to Abraham by the oak of Mamre, prior to the destruction of Sodom. Genesis 18:1-5
And the LORD appeared to him [Abraham] by the oaks of Mamre, as he sat at the door of his tent in the heat of the day. (2) He lifted up his eyes and looked, and behold, three men were standing in front of him. When he saw them, he ran from the tent door to meet them and bowed himself to the earth (4) and said, “O Lord, if I have found favor in your sight, do not pass by your servant. (4) Let a little water be brought, and wash your feet, and rest yourselves under the tree, (5) while I bring a morsel of bread, that you may refresh yourselves, and after that you may pass on–since you have come to your servant.” So they said, “Do as you have said.”
Abraham’s nephew Lot, also mistook the same angels for men. Genesis 19:1-3:
The two angels came to Sodom in the evening, and Lot was sitting in the gate of Sodom. When Lot saw them, he rose to meet them and bowed himself with his face to the earth (2) and said, “My lords, please turn aside to your servant’s house and spend the night and wash your feet. Then you may rise up early and go on your way.” They said, “No; we will spend the night in the town square.” (3) But he pressed them strongly; so they turned aside to him and entered his house. And he made them a feast and baked unleavened bread, and they ate.
Manoah and his wife initially mistook the angel of the LORD for a man – Judges 13:9-21:
And God listened to the voice of Manoah, and the angel of God came again to the woman as she sat in the field. But Manoah her husband was not with her. (10) So the woman ran quickly and told her husband, “Behold, the man who came to me the other day has appeared to me.” (11) And Manoah arose and went after his wife and came to the man and said to him, “Are you the man who spoke to this woman?” And he said, “I am.” (12) And Manoah said, “Now when your words come true, what is to be the child’s manner of life, and what is his mission?” (13) And the angel of the LORD said to Manoah, “Of all that I said to the woman let her be careful. (14) She may not eat of anything that comes from the vine, neither let her drink wine or strong drink, or eat any unclean thing. All that I commanded her let her observe.” (15) Manoah said to the angel of the LORD, “Please let us detain you and prepare a young goat for you.” (16) And the angel of the LORD said to Manoah, “If you detain me, I will not eat of your food. But if you prepare a burnt offering, then offer it to the LORD.” (For Manoah did not know that he was the angel of the LORD.) (17) And Manoah said to the angel of the LORD, “What is your name, so that, when your words come true, we may honor you?” (18) And the angel of the LORD said to him, “Why do you ask my name, seeing it is wonderful?” (19) So Manoah took the young goat with the grain offering, and offered it on the rock to the LORD, to the one who works wonders, and Manoah and his wife were watching. (20) And when the flame went up toward heaven from the altar, the angel of the LORD went up in the flame of the altar. Now Manoah and his wife were watching, and they fell on their faces to the ground. (21) The angel of the LORD appeared no more to Manoah and to his wife. Then Manoah knew that he was the angel of the LORD.
cf. Hebrews 13:2:
Do not neglect to show hospitality to strangers, for thereby some have entertained angels unawares.
This passage from Hebrews is probably referring to the above references in the old testament, where Abraham, Lot & Manoah entertained angels initially believing them to be men.
A verse from the New Testament which indicates the size of men and angels are similar: Revelation 21:17:
Then he measured its wall: one hundred and forty-four cubits, according to the measure of a man, that is, of an angel.