Min. age to ride alone (or with another child) is 7. My DD9 is asked constantly how old she is-which really "ticks" her off. She's only 4'-1" and petite. I told her I would make her a button that says "I'm 9-don't ask!"

She gets asked this
every time she rides TSM and MM alone.
Anyway, as far as our experience has been, it's 7 or they must ride with an adult.
Here are the height requirements from the DLR website
32" Autopia (must ride with someone 54" or tall) Note-My DD and her friend rode this together and even though they were both tall enough (49-51") they really couldn't operate the gas pedal properly. My DD wasn't very happy when they got off.
35" Gadgets Go Coaster; Matterhorn
36" Tuck 'n Rolls DriveEm Buggies
40" BTRM; Splash and Space Mtn; Star Tours; Jumping Jellies; Soarin'; and Tower of Terror
42" Grizzly River Rapids; Mulholland Madness; Redwood Creek Challenge Trail Brother Bear Show
46" Indy Jones
48" Screamin'; Orange Stinger (though this has changed and they know allow smaller kids to ride with an adult-the chairs are joined)
52" Malibooomer (still hoping my DD9 will grow tall enough before they take this down.)
54" Autopia-to ride alone
Also, in Redwood Creek Challenge Trail the Smoke Jumpers (zip line) has a max. height, something like 60" +/-
HTH.
