SEP IRAs

No - there are no catch provisions. The limitations are the same. 25% of compensation but no more than $51,000.

Employers can contribute up to a quarter of the salaries that each employee earns (25%)up to an annual maximum limit. For 2017, that maximum will be $54,000, up $1,000 from its 2016 level. That's the first rise in the SEP IRA limit since 2015,
For self-employed. the 25% refers to the self-employed worker's "net earnings" from the business. The net result of the math is that the 25% limitation on "net earnings" works out to 20% of your adjusted profit after the self-employment tax adjustment

A SEP is an abbreviation for a Simplified Employee Pension IRA. A retirement plan that an employer or self-employed individuals can establish.
The employer is allowed a tax deduction for contributions made to the SEP plan and makes contributions to each eligible employee's SEP IRA on a discretionary basis.
Contributions to SEP IRAs are immediately 100% vested, and the IRA owner directs the investments.

Unlike a Keogh, which must be set up before the end of the taxable year in which the plan is to be effective, a employer may contribute to a SEP (Simplified Employee Pension IRA) set up by the filing deadline of Form 1040 (generally 4/15/XX) including extensions.

Yes. You may continue to contribute to your Keogh or SEP plan if you have Self-employment income. You are required to receive a minimum distribution by April 1 of the following year in which you reach age 70 1/2 after age 70 1/2 if you are more than a 5% owner.

Some advantages of a SEP Simplified Employee Pension Plan are: Contributions to a SEP are tax deductible and your business pays no taxes on the earnings on the investments. You are not locked into making contributions every year. In fact, you decide each year whether, and how much, to contribute to your employees’ SEP-IRAs. Generally, you do not have to file any documents with the government. Sole proprietors, partnerships, and corporations, including S corporations, can set up SEPs. You may be eligible for a tax credit of up to $500 per year for each of the first 3 years for the cost of starting the plan. Administrative costs are low.

SEP is an abbreviation for a simplified employee pension plan.
Simplified Employee Pension plans (SEPs) can provide a significant source of income at retirement by allowing employers to set aside money in retirement accounts for themselves and their employees.
Under a SEP, an employer contributes directly to traditional individual retirement accounts (SEP-IRAs) for all employees (including the employer).
A SEP does not have the start-up and operating costs of a conventional retirement plan and allows for a contribution of up to 25 percent of each employee’s pay. Sole proprietors, partnerships, and corporations, including S corporations, can set up SEPs. Your employer's SEP contributions are excluded from your pay and not included on your W-2 form.