wow my grandpa is way stronger than me in armwrestling and sometimes faster than me too

I always lose my grandpa when we have armwrestling. his hand is very strong even now. I am 17 and he is 66. I remember in 2015 april when we were waiting for a train in railway station we were having a running race of going down the stairs and he surprisingly ran faster than me. I was 15 and he was 64 that time