Um, honestly, other than the last two ages, I would have to say this is wrong -_- Upgrading the age you're in ASAP is a surefire way to be screwed on any difficulty...normal not so much, but you're screwed trying it on Harder...
Honestly, I would say use the strategy of the last two ages from this guide, but just spam egg autos, club men, and the meteor special for the first three...clubmen make sufficient meatshields and can actually do a ton of damage if you can bunch them up (which tends to happen on Impossible, when the enemy is squishing you against your own fort, clubmen pile up and you have like 30-40 attacking at once)...they're also the most cost-effective unit in the game. Consider this: A dino rider costs 100 to make. Since enemies have supposedly 425% of their normal HP, it would take 4-5 dino riders without turret support (maybe 2-3 with, but still...). 2 dino riders costs 200, one kill nets 133. Losing battle there. CAVEMEN, on the other hand...while they're horrible without turret support, in large numbers or with turret support, they shine (doesn't matter what the meatshield is to a turret). With turret support, 3-4 cavemen is probably sufficient to take down a dino rider. 4 cavemen costs 60 gold. PROFIT.
Heck, this works on later ages too (particularly on cannoneers). 4 cavemen with turret support can take a swordsman, 43 can easily take a knight, 86 can probably OHKO a cannoneer if globbed together...also, consider cannoneers attack SLOW. Less dangerous than the fast-hitting Duelists/Melee Infantry. All these kills turn a profit...so honestly, cavemen are the way to go for the first three ages (I made it through the first three on cavemen + turret support easily...then screwed myself over by advancing).
