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In the Old Testament there was an entire order of men and women, known as Nazirites (“consecrated ones”), who were were essentially monks and nuns.

Numbers 6:2-4, 6-8 says they took vows of self-denial.

Numbers 6:5 tells us they had a distinctive appearance. John the Baptist was one of these (Luke 1:15), , as were Samson (Judges 13:5-6) and Samuel (1 Sam. 1:11).

The Nazarites were not Monks at all. They showed their dedication to God by obeying extra regulations for a limited period of time but being a Nazarite wasn't a person's vocation or job, as it is for monks. Nazarites were still part of the community of God in Israel. They didn't form their own communities or communes, with the exception of the Essenes, who were another thing altogether.

A Christian can have periods of fasting, for instance, without being a monk. A monk is a vocation, which is a supposed higher calling, yet all Christians are supposed to do all things--including working in whatever vocation that they have--to the glory of God (1 Cor. 10:31), and the plumber is no less holy than the monk.

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The prophetess Anna was basically what we would call a cloistered nun. Luke 2:36-37

She belonged to no order but was singularly called out as a prophetess, which was a special designation not typical in Israel (there were only a few women mentioned with such a title). Her dedication to God was admirable, but a nun, she was not.

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In the Christian age, Paul took a temporary Nazirite vow (Acts 18:18)

The vow was not a vocation, nor was Paul joining himself to some special order, away from the broader Church, nor was it a vow for life. The Nazarite vows typically had time limits while monks make vows for the rest of their lives. Nazarites were typically normal, everyday Jews who did normal, everyday things and worked normal, everyday jobs. Monks live in a commune away from normal life.

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...and recommended that others live celibate lives, consecrated to God.

Paul recommended that those who were gifted with singleness (meaning, they didn't struggle with the sexual temptations that are common to human beings) remain single, but again, that was for all Christians, not a special class. Consecrating lives to God was, again, for all Christians, not as a special group alone.

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He also set up an order of widows living the consecrated life after the deaths of their husbands (1 Tim. 5:3-12).

The so-called order of widows was a welfare program. The context of the widows in 1 Tim. 5 was about women who could care for themselves, marry and be cared for by a husband, or be cared for by their families. The "enrollment" was about being provided for by the Church, and it was only to be done for those who were godly in character and were not to abuse the help through sin that might bring reproach on Christ. The widows weren't just any woman who wanted to devote their lives to God, but only those women who were too old to be remarried and who couldn't be cared for by family first. Only these were "truly widows" and could be burdened by the Church (not in some monastery or nunnery apart from the Church).

Nothing Paul or the other examples cited supports monasticism, but only allows for some practices that are common with monasticism but which other non-monks or nuns can participate in.

Christians are called to be in the world, being salt and light to it, not to be "cloistered" away from it. Christians are called to be part of the community of believers that are gifted with many gifts, some being young women and some older women; some young men and some older men; and some being children. Monks are largely separated from the community of Christians, men being with men and women being with women, serving one another but not the larger body with many more gifts. Christians are also called to the calling of marriage as a normative practice, with marriage even being a test of leadership ability in the Church, which goes out the window with celibate monks. Christians are also called priests (the priesthood of the believer) in their everyday lives and vocations, while monks and nuns are considered more holy due to their vocations set apart from the world.

The Scriptures don't teach monasticism but presuppose Christians living in community with one another, serving one another and being served by one another, using their gifts to build up the Church and care for their brothers and sisters in the Lord. They are expected to have typical vocations, except for the teaching elder (pastor) who alone is set apart as being honored with pay for his work in the ministry, while welfare should be given only to those who cannot provide for themselves (the order of widows).

The Scriptures simply don't provide a basis for the Catholic practice of monastic life, which is why such a practice didn't become a "thing" for a couple hundred years after Christ's ascension.