Here are my suggestions:
1) Develop a net worth and an income statement (wage, expenses).
2) Project your net worth out with reasonable estimates on investment growth, income growth, debt paydown, etc. Hopefully you will achieve a period where 4% (or more conservative 3%) of your investment assets will cover your expenses. That is your FI date. Review to see if you are happy with this. If so, update and review quarterly or annually. If not, take actions (e.g. figure out how to grow income, how to trim expenses).
3) Once you do this as a habit, don't think about it too much.
4) If, and when you have a significant other, share this to make sure you guys are aligned.