If i take a low dose of levothyroxine (25 mcg) for life, would my thyroid become lazier/ slower? can this low starting dose work for hypothyroid?

No: Your thyroid wont become lazy or tolerant. The dose your on is a good starting dose and may be the right dose.

Hypothyroid: The cause of hypothyroidism is unknown unless you had exposure to large amount of radiation in the past. To see how we'll your thyroid gland is functioning you need to follow labs including tsh, t3, (liothyronine) T4 levels and that will determine your dosage of levothyroxine.

See a doctor: If you have low thyroid then you need replacement--like levothyroxine. If you do not, then taking that medication can be harmful. There are various possible causes for hypothyroidism, but they all usually get worse, so you can need more thyroid medication as time goes on.