"I know of no instances where a production had any big problem finding a young act to play an older counterpart. It’s all about the 'look' first. Casting directors start there. The look has to be right for the audience to believe that this is the younger version of the character. Once you have that 'buy-in,' you’re mostly there. The young actor’s talent then becomes important for complete believability," Mike explained.

According to the Hollywood insider, Tinseltown almost exclusively focuses on finding people who have acting experience. Even in the case of young actors.

"It’s a rare situation to cast an inexperienced actor, and work with them during production. That would slow down the production, and of course 'time is money' which is especially true in Hollywood."

Mike added, "Most productions are working under tight budget and time constraints, and there is an unwillingness to work with new talent. An exception would be an actor that is so 'special,' the production would be willing to put in the extra time and effort to make it work. That would be a rare exception, however."

There are many possible reasons why younger and older actors look alike. Probably the most important thing is that they have similar facial features. Though that creates a huge challenge: you have to find not only someone who looks like the younger actor but also someone who’s a capable actor in their own right.

Other things that make actors look similar to one another are similar hairstyles and dressing them up in clothes of the same style.

What’s more, if young actors are taught to mimic the movements and speech patterns of their older counterparts, you might genuinely think that they’re one and the same (unless the age gap is really big, of course).

Hadley Freeman writes in The Guardian that there are some other reasons why celebrities tend to look very similar.

According to Freeman, older actresses were very similar because they either had the same plastic surgeon or had the same procedures done. What’s more, stars used to have the same high-profile stylists and makeup artists.

But those aren’t the only reasons. Celebrity publicists are very image-conscious when it comes to their stars. So they’ll ‘allow’ only certain looks that change over time with trends.

That’s not to say that this is necessarily a bad thing; however, that does mean that actors have less of a chance to stand out and be original.