The idea is simple, but I like the design. Perhaps it would be more fun if a person could insert multiple entries (for example, holding a certain amount of BTC in a certain period, and then another amount in another period), that would be more valuable to see, IMO, as here the chart is essentially the same, and only the numbers in USD change based on how much a person is holding.
The first data point at this moment is from 23 February 2014 but I'll try to obtain more old data somehow. Cheers, mate.
There's data since the end of April 2013 on Coingecko:
https://www.coingecko.com/en/coins/bitcoin. Perhaps, you could use this to make the chart bigger.