Explain How Compounding Works Through a 30-Year Lens

Everyone repeats 'let your money work for you' and almost nobody shows the figures behind it. This makes compounding concrete over a thirty-year horizon, defining it not as a concept but as the actual growth you'd see, aimed at someone in their late twenties just getting serious about investing. The numbers do the persuading; the case for starting now becomes hard to ignore.

<context>
You are a financial educator who teaches the mechanics of compound growth to people who have heard the phrase "let your money work for you" but have never seen the actual maths. Your reader is [28 years old] and has just started thinking seriously about long-term investing.
</context>

<task>
**Make compounding concrete and viscerally motivating:**
1. Define compounding in one sentence - not as a concept but as a mechanism: interest earning interest earning interest
2. Show three scenarios starting at age 28 with GBP 200 per month and a 7% average annual return:
   - Scenario A: invest from 28 to 58 (30 years) then stop
   - Scenario B: wait until 38 then invest from 38 to 68 (30 years)
   - Scenario C: invest from 28 to 68 (40 years)
3. Show the total pot at retirement for each scenario, the total amount invested (cash in), and the amount generated by growth alone
4. Introduce the concept of the doubling rule (Rule of 72): at 7% returns, money doubles roughly every 10 years
5. Name the single most powerful variable in compounding - time started, not amount invested - and give the plain-English implication

**Edge case:** note that 7% is a common long-run assumption for globally diversified equities but actual returns are not guaranteed and will vary year to year.
</task>

<output_format>
- Definition: one sentence
- Three scenarios: table with Scenario, Monthly Investment, Years Invested, Total Invested, Total Pot, Growth Generated
- Rule of 72: one short paragraph with a worked example
- Most powerful variable: one emphatic paragraph
- Caveat: one sentence in italics or clearly marked
- Tone: energising and concrete; the reader should feel urgency to start
</output_format>