Age is no Problem for me. as long as the rules are known and no one starts crying.
The worst are players turning the Fluff into brezels to justify their PG Lists as a Fluff List aka the 2/9 Chaos SM List is a fluff List cause its undiveded and/or Black Legion.
A hate this and i have hard times not to take their Rulebook and Codex to beat them until they are crying for their poppy and momy.