Doesn't matter as long as you are buying from a reputable shop. Check the tyre for a 4-digit code on the sidewall, it will look something like XXYY where XX is a number from 01 to 52 and YY is a number from 15-25 (hopefully). That tells you the tyre was made in (week number) of (year). Try to find a tyre no older than 1 year from your date of purchase, e.g. 4024-5224 (i.e. made in last 3 months of 2024) and 0125-4025 (made in 1st 10 months of 2025).
Anything older than 1 year, I wouldn't buy even if the mechanic said it's fine to use.