Is 5th Edition Old School?

My Perspective
Wizards of the Coast and Hasbro have done an excellent job listening to "old school" gamers and 5e is much closer to older editions of the game than 4th Edition was. From a marketing stand-point, 5e maybe hits the sweet spot between appealing to as many hobbyists, old and new school, as possible. Prompted by Mike Mearls' Greyhawk Variant and recent release of Unearthed Arcana: Greyhawk Initiative, I am once again comparing 5e to my concepts of an "old school" game. I now have enough experience with 5e that I feel comfortable commenting on that from my personal old school perspective.
Over the decades since the beginning of the hobby initiated by White Box, gamers have come to expect new and different things from their rule system. PC individualization and ability to survive have increased over time when comparisons are made between older and newer editions of the game. The White Box PC level progression can be stated as "zero-to-hero-to-superhero". In contrast, WizBro era editions tend to start PCs at higher levels of relative power and then progress more quickly to super power status and beyond. A combination of the ascending Armor Class mechanic introduced in 3e, Ability score bonuses and Feats can drastically increase the damage output of PCs. The result is that today's "super hero" PC has dramatically changed the "feel" of the game for many older referees (myself included).
The relative power level of a 1st level character is dramatically higher in 5e than White Box as evidenced by the chances to hit an enemy in melee. Using the Alternative Combat System found in Volume 1: Men & Magic, the 1st level PC (of any class) has to roll a 12 or higher on a d20 to hit Armor Class 7 (Leather Armor), a common AC for many "monsters". Rolling a 12 or higher on the twenty-sided dice gives a 45% chance of success (high Strength does not increase chance to hit in White Box). So a little less than one-half the time the PC hits the monster.
In 5e To-Hit numbers are determined quite different from using the matrix of White Box (and early AD&D). The 1st level PC has a base AC target number to hit rolling a d20. Leather Armor gives an AC of 11. To make an attack, the player rolls a twenty-sided die and adds any Ability Bonus (usually Strength bonus for melee) and Proficiency Bonus (+2) for a 1st level character. Creating an "average" PC by-the-book in 5e likely results in a Strength Ability bonus of  +3 (for a Fighter), so the total adds to the d20 roll is +5. In order to hit an AC of 11, the fighter needs a score of 6 or better (11 minus 5 equals 6). This is a 75% chance of success - much higher than that of the White Box Fighting Man.
Player Character power level is only one aspect of play affecting how one feels about the game. "rulings not rules" is another commonly held believe regarding "old school" play and in this 5e is a return to a more rules lite, loose system allowing referee fiat to a greater degree than other WizBro era editions. The 5e books are written with a number of options in place which can be accessed or ignored by the referee allowing customization of the game while staying technically within the rules as written. Whether this goes far enough to satisfy the individual referee is a question each must answer for themselves.
The 5e system currently comes in two flavors: the full system found in the three core hardbacks and a "Basic" system found online as free downloads. The Basic 5e is a simplified and cut-down version of the full game and it includes no art. In effect the material it does contain seems more consistent with an "old school" approach to the game than the full version. The Basic game limits character class selection to the basic four - cleric, fighter, rogue and wizard; it limits races to the traditional human, elf, dwarf and halfling. There are no warlocks or sorcerers, no dragonborn or tiefling, and no feats. Rogue Comet has taken the Basic 5e material and re-imagined it as Dungeonesque which is marketed as 5e optimized for "old school" play.
I have not used the Greyhawk Initiative variant rules, but reading them I am reminded of how the Perrin Conventions (1976) were used together with White Box to give more structure and tactical focus to combat using the LBBs. The Greyhawk Initiative system uses a count-down mechanic that likely results in ranged attacks going off first followed by movement, melee and spell casting. Each player must declare at the beginning of each round what they intend to do. According to Mr. Mearls, it may also make healing a bit more difficult to use in combat (and thereby give a more deadly game?).
Ease of character generation and the ability to handle frequent character death go hand-in-hand in my opinion and I find 5e restrictive in this regard. Healing is frequent and readily available in 5e reflecting more recent popular trends in game design. PCs, and NPCs using similar rules, are difficult to kill using all the "get out of death" options available. PC death, when it happens, is often the result of a "perfect storm" of everything going wrong rather than a calculated gamble on the part of a player. The incremental reduction of White Box PC hit points allows the player to calculate how long their PC is "likely" to last in a fight. The player can quickly "do the odds" in their head and make decisions based on known probabilities. The "save or die" mechanics of some traps and poisons is an obvious exception to this "predictability" in White Box and while perhaps feeling "unfair" to some, maintains an element of "fear" in the game. A dead PC can result in a period "out of game" for the player forced to generate a new character that is directly proportional to how much time needs to be spent in chargen. Thus I think quicker is better in a game likely to have high PC mortality rates.
All these aspects combine in a game system to create a "feel" at the game table. If the referee desires an "old school" feel and has players who also buy into this style of gaming, can 5e deliver? I am still debating this, but also finding myself leaning ever further away from saying, "yes, it can". I like that older modules can be played with 5e (more easily than with 4e or 3e) and that WizBro is publishing new material inspired by the old modules. I like Backgrounds and the fact that Feats are optional. I like Advantages and Disadvantages as a mechanic and the general looseness and brevity of the rules (and the fact that there are ONLY three books). I am less happy with healing, PC mortality and "power level".
The 5e rules give a nice game, an enjoyable tabletop adventure game experience and the published play-aids are entertaining and well written for the most part. WizBro is doing a very good job with the 5e product in my opinion and I am quite pleased over-all. Perhaps it is inconsequential whether 5e is "old school" or not.  Maybe all that matters is that it has appeal to a self-styled "old school" referee.