What kind of grandma is 50 year old? Was she pregnant at 5?

Most grandmothers, by the time you are able to use bitcoin normally ~ 15 , are usually above 60 or near to it.

By the time you are adult they hit 65 or even 70.

60 year old grandmothers can barely use anything other than TV, oven, and washing machine. 

We need a new generation of old people to be bitcoin, and it wont be even your parents

I don't think so. Only for 6 years of life bitcoins has only here on bitcointalk more than 500 000 users. To not tell for others who don't prefer to be part of this forum. Only China has millions between users and miners. the spread will be every day much more than the previous. The results and even the last bubble of bitcoin is a clear signs of this spread. It was an increase of demand from China which is behind the increase of price for about 100% and its drop at 50% (at least this is the most probably reason told by most of the analysts). The remaining 50% which is reflected in the actual price of bitcoin compared to the one before the bubble is a clear sign of the increase of the people which know and want bitcoin. And this demand are mostly new people which want to be owner of some bitcoins.

Lack of real Bitcoin infrastructure in the places where people actually spend money - i.e. supermarkets, bars, nightclubs, strip clubs, coffee shops, etc.

Amazon accepting it would be a huge thing. It will take more corporate adoption before people are comfortable with it. Too many people still hold the negative associations from the 2012 era when all people were hearing was the 'deep web' and 'Silk Road' - as well as other lovely buzzwords like 'hitmen' and 'drug dealers'.

Bitcoin needs a bit of positive PR and a few killer apps.

I believe the biggest reason besides lack of knowledge is fear, people are afraid of change, plus the fact that bitcoin are not physical unlike printed or minted currency. The average individual doesn't understand how digital currency works even though their own governmental currency is basically digital. The tangible will overshadow the intangible even if it is just an illusion.

another reason, it's because some do not know about the advantages(low fees) and some simply think that fiat can do everything already, they do not see it as a real alternative to usd or euro

can you blame them?

I think fear. U'd be a bit of adventurer to use this currency

Well per example my mom, I tell her what is Bitcoin, how you get it, how it works.

Ans she still don't get it. So that's is why people don't get BTC.

It needs some good explanation. Maybe a little good conversation while having coffee. Or, you can send your Mom some bitcoins then tell her how you can spend this and how you can earn some of this. That will be a good start. If people see that they can spend this kind of money in real world that will be the time where they will be interested in something.

Before trusting bitcoin people must know what is bitcoin. I believe the lack of knowledge on bitcoin is the bigggest stopping off people using bitcoin.
People will hold bitcoin until they get some profit. Holding bitcoin will not affect the flow bitcoin as lot of bitcoin are in flow and lot of bitcoin are generated in every 10 minutes.

Government factor is the one thing and the most important factor that I believe is that the price fluctuation of bitcoins is too difficult to handle. Looking at the price fluctuations people hesitate in investing or using bitcoins as they feel that they would have to suffer from losses in the near future but if the price is stable than more and more people would start using bitcoins.