I don't think its possible for me. I have the worst habit of starting characters over, and I don't even know if I have made it to level 30 before beating the game, the few times that I have. I'm currently at hoover dam right now at lvl 28, and 28 hours of playing time. I wish I could stay with a character that long, but i have the worst itch to always start over, or if I waste perks.

How do you all keep playing through, to reach lvl 50?

This is just me, but I do all the side quests, faction quests, DLC, exploring, etc, first, and save the main quest for last.

Make a character you really like. Figure out an awesome backstory and take 'fitting' perks (like if he's a rancher character, take the Cowboy perk, Home on the Range etc...). That way it means you can never make a 'wrong' decision on perks because they're more a story decision than a math stat. Getting totally immersed in the story of that character is what gets me through all the quests needed to get to level 50.

How do you NOT get to level 50? I do all the quests I can and the DLCs. See the character to the end etc. etc.

It isn't too hard really.