No, postponing evolution does not cause a Pokemon to level up any faster. The amount of Experience required to reach Level 100 is the same across evolutionary chains. So, Bulbasaur requires 1,059,860 Exp to reach Level 100 and Venusaur requires 1,059,860 Exp to reach Level 100. Since they both require the same amount of Exp to reach Level 100, and since they both gain Exp at the same rate, they both take the same amount of time to level up.
The game calculates stats dynamically based on a set of values the Pokemon has, such as its Base Stats, IVs and EVs. Since the calculation is made dynamically, it doesn't matter when any one of these values is changed, the end result will always be the same. For instance, if you have a Level 5 Pokemon with a Speed EV of 0, it won't matter if you level it up to 50 then increase its Speed EV 252 or increse the EV before leveling it up because, in the end, it will be Level 50 with a Speed EV of 252, and those are the two numbers that will be used to calculate its Speed stat:
(Base Stat x 2 + IV + EV / 4) x Level / 100 + 5
(Base Stat x 2 + IV + 252 / 4) x 50 / 100 + 5
(Base Stat x 2 + IV + 63) / 2 + 5