When you level all 18 skills to 100, you can't gain any more, so you reach the maximum level of 81. OTOH, you can just work 3 skills (Like Archery, 1H, and Light Armor) and set your own cap at around 30. (Depending on starting bonuses.) Just don't work other skills, at all, and you won't go up in level. neither will any of the NPCs, so this freezes the game at that level, while you go around killing everything, running all the quests, and spending your money. (In shops, you'll eventually earn Speech XP.) Or, you can change class, and add new skills to augment your first ones, while the game also goes up some more tiers. This is tricky, though, because you want to save the fast levelers for later, when you need more XP to advance. Block, for instance, is good to get over with early, and Illusion, since it becomes less effective as NPCs level past it.
So, say you do a Spell/Shield combo to start, with Destruction, Block, and HA. About level 30, you're nearly static, so you can start working Conjuration, and 1H with Bound Sword (An incredibly fast leveler) while HA continues to catch up. Or, save Crafting for this point, when you've already got your weapon skill/s up to 100, and the only way to increase damage is to improve your gear. This is getting beyond the "Pure" build, but what I'm trying to say is, you can start off fairly pure, and then branch out once you have a solid base well ahead of the NPC curve. The greatest advantage to this is you never really have to grind. Just stick to the 3 skills (optimal, if you're filling out the trees. Otherwise, you find yourself with perks you don't have the skill to spend, or skills without the points to perk, but you can do 4-5 if some of them are half trees, or splashes.) and ignore the rest.
The main problem I have with Pure builds is Speech, which I avoid by staying out of shops for the most part. You have to buy a lot of your spellbooks, and higher level robes (Archmages' and Morokei are a Starter Set, Master robes are far superior) but I use a lot of spells that can be found, or gotten from quests (Flame Cloak from the Scorched Cape, Flaming Familiar, Detect Life, Bound Sword, and Bow...) I also have a Follower to open chests, so I don't have to worry about Lockpicking.