I would even sign 2 players around the age of 30. Or is their an age cap for B teams?
I'm not sure if there is an imposed limit. I believe Barcelona self-adhere to not having anyone older than 26 or so. I read it somewhere years ago but don't have a source for you.
I recall watching Villarreal B in Segunda in 2012 and they had a 30 year old player (Gerard Bordas) so it doesn't seem to be a LaLiga statute (unless things have changed in the past 8 years).