1 Samuel 1:22

But Hannah went not up
For women, though they might go if they pleased to the yearly feasts, yet they were not obliged to it; whether she went up at the time for her purification, and for the presenting and redemption of the firstborn, is not certain; some say the Levites were not obliged by that law, the perquisites of it falling to them, and so did not go up; others that she did, though it is not expressed, the Scriptures not relating all facts that were done; though by what follows it looks as if she did not:

for she said unto her husband, I will not go up until the child be
weaned:
which, according to Jarchi, was at the end of twenty two months; but others say at the end of twenty four months, or two years, as Kimchi and Ben Melech; and sometimes a child was three years old before it was weaned, and sometimes longer, which very probably was the case here; (See Gill on Genesis 21:8). Comestor ^F4 observes, there was a three fold weaning of children in old times; the first from their mother's milk, when three years old; the second from their tender age, and care of a dry nurse, when seven years old; the third from childish manners, when at twelve years of age; and that it is this last and metaphorical weaning which is here meant, when Samuel was twelve years of age, and fit to serve in the temple; but the proper sense is best, since she is said to bring him when weaned: her reason for it seems to be this, because had she went up with her sucking child, she must have brought him back again, since he would not be fit to be left behind, and would be entirely incapable of any kind of service in the sanctuary; and according to the nature of her vow, she could not think of bringing him back again, after she had once entered him there:

and then I will bring him, that he may appear before the Lord;
and minister in the service of the sanctuary in what might be suitable to his age; there and then she would present him, and give him up to the Lord, as she had promised she would:

and there abide for ever;
that is, as long as he lived; for her vow was that he should be a Nazarite all the days of his life, and be separated to the service of God as long as he had a being in the world.