[Spoilers Extended] The ages of Alicent and Rhaenyra in HOTD

In my opinion, they could have kept Alicent and Rhaenyra's friendship and still have them be different ages (but a a little age gap compared with the book, maybe 4 o 5 years). In Japan there is the concept of "senpai" or senior, that is, an acquaintance or friend who is one or more years older than you and for that reason you owe them honor and respect.

They could have done something like that with Alicent and Rhaenyra, it wasn't necessary for them to be the exact same age, even if they wanted to make Viserys look like a dirty old man.