I know this a novice question and the answer could be obvious, but despite searching I still can't figure it out.

I am running multiple age groups to a landing page with facebook ads. Each age group has its own sub id. When I get a conversion on the landing page, is there a way to see which sub id it came from?

On you destination url put the age group. Example: KW=Age20-25

To expand further, if you are doing multiple pictures then you would ad the picture at the end. Example: KW=Age20-25_Picture1

You would do this for each age group. It's tedious work, but you should be able to track correctly this way.

Let me know if this helps