Yoga is making you old
First of all, some of my bestfriend's friend's are yogis, so I can talk about them. They practice yoga religously (not literally - though some actually do) own/run yoga studios, are long-distance runners, or road bikers. My intention is not to piss you off or disparage your art (as my title perhaps already did). Additionally, yoga, running and biking all have some fantastic attributes that are healthful and beneficial, and if the options are yoga or couch-surfing, the answer is yoga by a country-mile. The flexibility and balance that yoga promotes makes a great addition to any resistance training program.
That said, you should be aware that if you practice yoga, or run or bike long distances, you are prematurely aging your body. Here's why:
Yoga (in the exercise sense, not the spiritual one) - Yoga is touted as both a physical and psychological exercise that is based on slow, controlled movements, and slow deep breaths, which is great... if you want to move slowly. Just like sprinters, football players, etc, train their muscles to be quick, so that they can run fast and react quickly to stimuli, you are training your body to do the opposite. In the wild, you would be the first one picked off by a predator (or maybe the second, after that guy in your office who's always sick), in the 'cizilized' world you won't be able to jump out of the way of a millenial who is updating their Snapchat while biking to the farmer's market.
Therefore: old body = slow moving = yoga
Long distance running - Frequent long distance running hits you even harder than yoga. Endurance-based cardiovascular training decreases the total Testosterone (T) and Free Testosterone production in the body for up to 1 week after a long run. It is also increases cortisol levels (stress hormone) within the body. For the women, before you think, "great! I don't want hairy knuckles anyways", you should be aware that Testosterone is an important hormone in your body as well, as it works in concert with Estrogen and Progesterone to regulate your system. Why less Testosterone is important to EVERYBODY is that it is the main hormone responsible for muscle tone (along with growth hormone), and it regulates collagen production and lubrication in your dermas. Decreased T levels in your body can contribute to dry, weathered looking skin.
Thus: old body = diminished muscle tone & leathery skin = long distance running
Long distance biking - Want a hump that would make the Quasimodo envious? Go for long rides on the weekends and then dont stretch and do resistence training. Before I dive in to the reasons long distance biking will make you look like a turtle, I should mention that at least biking will strengthen your leg muscles while improving your cardiovascular system, albeit in one of the smallest ranges of motion possible (this is also part of the problem). The standard biking position is forward leaning, hands on the front of the bars with arms bent, elbows below your shoulders. Your lower back is rounded (as is your upper back), and your neck is extended forward, with your chin looking upward. Now what could possible be the issue with this position? 1. Your rounded shoulders mean your chest is engaged, as are your biceps. These will tighten, creating rounded shoulders and arms that have a bend when hanging naturally. 2. Your lower back is rounded. If you were on your back, you would need to use your core strength to maintain this position, however, with your feet underneath you, this position allows your core and abs to relax, or worse yet, causes you to push out against your abs, teaching your core ultimate laziness. 3. When bent over your handle bars, the forward-head-posture that is necessicity (so that you can see where you're going), excentuates the hunch the you are working so diligently to build.
Result: old body = every day is hump day = long distance biking
If you are reading this article and are not currently exercising regularly, I absolutely recommend any of these activities. All of them provide benefits that not doing them cannot give you. However, if you ONLY currently do one of these activities, I urge you to encorporate resistance training to fight the effects of aging (whether natural or self-inflicted).