It's usually hard to persuade the older generation to invest it cryptocurrency and that is because most of them are not tech savvy and it is not good to invest your money in something you don't know. Try to enlighten them about the technology and how it is the future before you advise them to invest.
Yes, to just give advice and explain I think it is still very good to do, but in this case there is no need for persuasion to invest right away, let the parents' intentions drive their minds to invest and ask us, I think that is the way to go much better than outright persuading him to invest.
I believe that forcing someone to make an investment is a wrong thing, rather discussing and trying to explain what bitcoin and altcoins represent could be the best approach to intrigue and therefore allow them to make the first choices.
I also think that new generations of investors will have no problem juggling these technologies.