I’m working with doctors at the moment in a similar area. eGFR is well-known to decline at approx 1 point per year after age 30. You’re fine.

Here’s just one source: “After the age of 30 years, glomerular filtration rate (GFR) progressively declines at an average rate of 8 mL/min/1.73 m² per decade.4”

https://www.racgp.org.au/afp/2012/december/ckd-in-the-elderl...