Pokemon-go – Are wild Pokémon capped at level 30

Like Samthere said, you can delay indefinitely, however id recommend keeping one Pokemon high to take gyms with. Don't power it up more than you have to but keep it high enough to get at least a few gyms. The extra star dust and coins you get should be worth the candies and stardust you spend to keep just one Pokemon high. I usually get rid of anything with a CP meter under 90%. It's probably good to set a goal like level 25, otherwise you probably will delay it indefinitely. Lastly, go ahead and evolve any Ratatas and Spearows (or other really common ones in your area) you can for the experience. Their evolved forms max out pretty low so they aren't really viable later, otherwise leveling will get really slow unless you are hatching eggs left and right.

My data isn't complete as I haven't been actively keeping track, but here is what Iv'e found. Once you reach max CP for any Pokemon at your level, every subsequent level allows you to power up said Pokemon twice. Each power up grants 20-60(level 4-16) CP based off of the Pokemon's initial power and player level. My Lapras maxed out at 971 at level 11, 1056 at level 12, ~1140 (forgot screenshot) at level 13 and 1267 at level 14. +85, +~90, +~120. I have since run out of Lapras candies so i can't pursue this information further until i obtain more. I'll attempt to gather more data using a more common Pokemon later (Eevee evolution probably) and edit when i can, but the stardust needed is hard to maintain.

How this relates to the question:

The encounter CP is a random number between lowest possible (10 in 1st evolution) and maximum possible. From the data we can see that the max CP does increase incrementally so as a result encounter CP will increase at the same rate.

In conclusion, while it is more effective to power up and evolve Pokemon later, the max CP increase seems to be mild enough that from level to level the difference isn't insurmountable.