This simply isn't true. Not even slightly. Moyes did build a young squad, with arteta, Fellaini, baines, jags, yakubu, lescott etc all 24 or under when signed. Add in gosling, Rodwell, anichebe etc and you'll see that the team circa 2008/9 was probably significantly younger than this one. Its a bit easier to build a young side when you can splash £28m on one player than when you go 2 years without making a cash signing though, so it's not surprising that moyes couldn't keep doing it.
For all the supposed youth orientated approach, it's worth noting that Howard and barry have just been asked to complete 180 minutes in 3 days with a combined age somewhere around the amount of goals we're set to concede this season. We also picked 4 central midfielders on the bench rather than promoting an attacking youth prospect. Look at how moyes used Baxter, vellios, Mcaleney, Chadwick etc as part of his squad - Martinez has only given (very limited) opportunities to browning from our academy that I can think of.