I have a daughter that entered religious life at 18, but her preparation for her entry happened over many years. She was careful to grow in virtue, practice charity (especially in the home and towards her parents) and was careful in performing her daily duty. (In study hall, spend your time studying your school subjects!) She did not date. She did not daydream about being a religious (meaning spending time reading brochures, web pages, blogs, or forums). She only did what was necessary to advance in that regard. She was busy all the time, praying, working or recreating with others. When she entered, she was ready. She shared that her last year in the world was harder than her first year in religious life. The adjustment was fairly easy for her.
Yeah, and training yourself to eat one meal a day? I don’t agree with that. Monasteries don’t do that. Rather, make sure you are temperate in your eating.