How do I summon something at all entities with a certain scoreboard value?

My friends and I are making a PVP map and we’re working on the summoner/mage class, which summons things that deal damage at the position of a projectile. For testing purposes, I’m making a snowball that summons lightning at its position. I have an objective called age that counts up every frame for every snowball, and the lightning will only be summoned after the snowball’s age increases to a certain value, to stop the lightning from spawning on the player and damaging them (for testing purposes, that "certain value" is 20). I have an objective called numbers which simply stores values (this is where the aforementioned 20 is stored). Right now, I have execute as @e[type=minecraft:snowball] if score @s[type=minecraft:snowball] age > 20 numbers run summon minecraft:lightning_bolt
but instead of summoning the lightning at the snowball, it summons it at the command block. How can I fix this?