At 2 years old we switched from months to years. Babies do a lot of growing in 24 months so it conveys developmental milestones by giving months even past 1yr of age; a 12 month old will be very different from a 23 month old but both would be 1yr olds. It’s too complicated to try and do decimals for each month past 12mo, for example a 13 month old would be 1.08 years, but no one talks like that. Past 2yrs, once she reached the 1/2 way then I add it on for 2.5 until she’s 3, etc. Past 5 years the 1/2’s probably aren’t necessary any longer, then we can just say 5, 6, 7…