While individual differences in children are very large, I think children as young as early four years old could play it
Since 2011, WotC has released about 40 Commander precon sets (many with 2-4 decks each), plus entire sets dedicated to Commander staples and new cards for the format
Incredible, Super Stretchy Buzz Lightyear, On the Way Jessie, Lively Cowgirl Jack-Jack Parr, Incredible Potential The rulebook does a solid job of breaking down the finer points of play, and there are also official videos you can watch online if you're more of a visual learner
No longer a threat to anyones general, Riftsweeper was unbanned right after the release of Planechase in September 2009
The new set boasts a massive setlist of over 200 cards, including many new VMAX Pokmon for players to collect