the biggest sign I found was the difference when I complete the sum of Current Year - Year of Birth = X
Each year the answer seems to grow larger and I've not found a method to reverse this process yet.

Age isn't something which particularly matters to me, the main side effects of it are not the impact on me but on others, I'm well aware that it's unlikely I will be over 50 years old and have both or even one of my parents still alive, I'm gravely aware that my brother is both older than me and enjoys recreational drug use, his partner while older again also has a family history of degenerative cognitive defects in later life, with almost 100% of the female members of the family succumbing to them in relative youth, haha, it also reminds me that my cunt/ex wife is 6 years younger than me and will likely live to see a Star Wars movie + Stand alone film which I will not get to experience, unless Karma actually exists and she is consumed by a goat at some stage in her life.

But yeah.... how has my age impacted me? People trust me slightly more now when it comes to repairing PC's than they did when I was a little brat teen that is for sure, now I've got a face which suggests I'll fix it... rather than I'll steal it to download porn.... even though under the face I will still use it to download porn if my own laptop is out of power and something is required!

....

My age also impacts some of the way I refer to things as the previous paragraph should not have the term download in it, that is a throw back to being alive in the 80s/90s when downloading was a thing and the concept of streaming 1080p porn was just a pipe dream of the future... fuck it, I remember downloading porn... pictures...

you are under 20

While you still have any amount of the word "teen" in your name you cannot really look at others yet and think they haven't grown up.

If your joints are hurting at such an early age, it could be inflammation from the foods you eat, like anything grain based, I would investigate that if I was you, also some supplements can reduce inflammation, if this continues it could be arthritis for which exercise and a non-inflammatory diet are the only controls       

Time seems to pass by faster as we get older due to our logarithmic minds. It's just perception of time difference. Plus, age (the number) is just a reference point from the moment of your birth to the current moment, or memory. The age doesn't matter so much (if at all), what matters is the aging process or how long our bodies can "enterain the mind" so to speak.

Question - Would you rather be 40 and feel like you are 20, OR, would you rather be 20 and feel like you are 40?

I agree to a point.  If you're very good at persuasion and convincing, it's not always a waste. 

I'm just way taller than humans were designed to be and after years of athletics my joints are suffering for it. I take glucosamine which helps and avoid stressful exercises these days.

I used to know the signs of being old, but I can't seem to remember anything.

I’ll be 36 in August but everyone swears I’m 20-25. Some even say 19. They’re shocked when I tell them I’ll be 40 in 4 years. I still have to show my ID if I ever buy beer. But I know I’m getting old regardless if my body shows it or not.

My back hurts all the time, crows feet, hates today’s music, tv shows, games and movies. Hate the way all the kids today have to abbreviate everything on the internet and I have no idea what they’re talking about.

Yeah being really tall has its issues, looks like your doing some of things you have to do to control the inflammation anyway, I still suggest cutting out foods known to cause inflammation and see what happens, if nothing changes go back to them, you have nothing really to lose, but a lot to gain, goodluck     

People parking on my lawn really annoy me now :(

But I'm far more patient in traffic :)