So, does that mean the 10 year old billionaire is now 22?
No, that's not how aging in comics works. It's all up to Lord God Dave whether to advance the clock or not, and at what rate.
Quite a few strips (Peanuts) never age at all, some at a very slow rate, and others are almost following the Real World calendar. (Funky Winkerbean, et. al.)
IMNSHO Sheldon should have advanced slowly in age a little, maybe 12 to 13 by now - eventually they can start doing High School gags and the Graduation Saga, then off to College...
And eventually Gramps won't be around anymore, but that can be delayed a long time...
There's lots of story potential there, it's all in where Dave wants to take it.
Dave, I want to personally thank you for a simple thing - the little buttons at the top of the page where you can go back to 1, 2 and 5 years ago and read the comic.
Wonderful idea, and I have derived much pleasure from it.