The description of the Ready action states, in part:
When you ready a spell, you cast it as normal but hold its energy
Does this mean you could cast a fire bolt spell, hold its energy indefinitely (as long as it doesn't break concentration), and light up like in Skyrim?
That doesn't seem right to me; am I mistaken?
Two reasons. First of all, RAW doesn't mention any effects of the spell being effective while it is being held. There's no fire before the spell is actually released.
The more significant reason is that you can't hold a spell indefinitely; any readied action will be lost at the beginning of the character's next turn. See the Player's Handbook Errata: