Help a noob - Castle age

Hi guys! I've recently come back to AOE after a 10 years pause. Got into DE and been watching some YT videos like Spirit of the Law and Hera. After losing several online matches, I set myself to the task of defeating the Hard AI.

I feel I've got a good grasp of DA build orders, and can reasonably push some Feudal raiding with 5 - 7 units (be it m@a or archers), while somewhat avoiding idle TC/villagers.

My issue is mainly in Castle Age. This is when I lose momentum and start to fall behind. Between 3 TC booming, caring for unit, blacksmith and University upgrades, pushing for the relic war, building siege, castle and additional military buildings, 5 minutes have passed and my opponent is well back on his feet. My army usually ends up growing but idle, and when I try to use it, my opponent has already massed counters.

There on, everything goes downhill. I find it hard to addapt and respond, and find myself quickly overwhelmed.

Is there any tip, guide or advice specifically regarding to castle age you can give me?

Thanks in advance!